Intelligence & Psychological Testing

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Individual Differences

Intelligence & PsychologicalTesting

An undergraduate psychology course about Individual Differences

Last updated: 02 Aug 2005

Background

Intelligence links

Introduction

Why study intelligence? What do you think about intelligence?

What is intelligence? Many definitions...

History

Key players in the history & development of intelligence

Intelligence Quotient

Understanding & Interpreting IQ

About IQ Tests & IQ Testing

Theories of Intelligence

Sternberg's Triarchic Theory of Intelligence Intelligence as Speed of Processing

Gardener's Multiple Intelligences

Measurement, Method & Testing

Psychological Testing versus Assessment Essentials of a Good Psychological Test

Wechsler Adult Intelligence Scale (WAIS) - Example of an Intelligence Test

(+Tutorial 2)

Causes & Correlates of Intelligence

Nature vs. nurture in human intelligence

(causes & correlates)

Psychology of Intelligence - Recommended Links

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Intelligence

Psychology of Intelligence

Recommended Links

Last updated:02 Aug 2005

Intelligence - General

Similar intelligence courses & online texts

Online articles about intelligence

Intelligence - Specific Topics

Can machines be intelligent? (artificial intelligence)

Birth order, family size, & intelligence

Online & commonly used IQ tests

Intelligence tests & cultural bias

Multiple intelligences

Emotional intelligence

Flynn effect (IQ has increased over time)

IQ & criminality

Intelligence & Psychological Testing - PRACTICE EXAM (7pg MSWord .doc)Note this practice exam overemphasizes psychometric information about testingcompared to what will be in the real exam.

Similar Intelligence Courses & Online Texts

Intelligence - 1st year psychology lecture notes by R. G. Tonks, Camosun College

Chapter 6: Intelligence [Learning Objectives] - Foundations of Psychology (3rd ed.)

Intelligence Testing - Dr. Bruce Abbott - Indiana University-Purdue University Fort

Wayne The Personality Project - Recommended Readings in Personality & Ability

Online Articles about Intelligence

"Intelligence" articles - Encyclopaedia of Psychology

Controversy follows psychological testing [history of intelligence testing] - APA

Monitor APA Taskforce report on Intelligence - Press release (1996)

Frequently Asked Questions about IQ - Nicologic Intelligence Tests

What became of Albert Einstein's brain? (Neuroscience for Kids)

Recent intelligence articles in APA Monitor (Feb, 2003)

Ideas on Intelligence - Great Ideas in Psychology (useful points focusing on different

causes of intelligence) Two Views of "The Bell Curve" - pro- and con- book reviews of Herrnstein &

Murray's controversial "The Bell Curve: Intelligence and Class Structure in American Life"

Gottfredson et al article - summary of what is known about intelligence, signed bymany well-known psychologists, but mostly those from the "genetic" and"general intelligence" spectrum [.pdf, .4MB]

Can Machines be Intelligent?

Can a machine be Intelligent ? Class Debate - Issues and Ideas

"Artificial Intelligence" articles - Encyclopedia of Psychology

Overview of artificial intelligence

ArtificialBrains.com - includes a project to build a robotic cat

Ray Kurzweil - artificial intelligence guru; website has a variety of relevant topics

Foundations of artificial intelligence - the big issues (hefty!)

Google search on "artificial intelligence debate"

Birth Order, Family Size & Intelligence (Week 5 Tutorial)

Recent study finds no direct link between birth order, family size & intelligence

Birth order & intelligence - www.drspock.com

Google search "birth order intelligence" and "family size intelligence"

Intelligence Testing & Cultural Bias

Cultural bias in intelligence testing

Chitling Test of Intelligence (short form, 15 questions)

Redden-Simons "Rap" Test (12 questions)

The Australian/American Test of Intelligence (10 questions)

The Original Australian Test of Intelligence (10 questions)

Stalking the Wild Taboo - huge list of references

Intelligence tests & culture bias - Google Search

Multiple Intelligences

Multiple intelligences links - comprehensive list

Multiple intelligences - Google search

Emotional Intelligence

Emotional intelligence - Google Search

Your Emotional Landscape - Center for Emotional Leadership

Flynn Effect (IQ has increased over time)

Flynn Effect (IQ has increased over time) - Google Search

IQ & Criminality

Low IQ May Prevent Inmate Executions - newspaper article

Wechsler Adult Intelligence Scale (WAIS)

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Individual DifferencesWechsler Adult Intelligence Scale Last updated:Intelligence (WAIS) 13 Apr 2004

Brief information about the Wechsler Adult Intelligence Scale

WAIS Scales

Interpretation of the WAIS-R

Discussion question

More detailed notes about the WAIS-R WAIS-

R psychometrics (reliability & validity)

Brief information about the Wechsler Adult Intelligence Scale

David Wechsler designed intelligence tests made up of items that are appropriate for a wide range of ages.

There are three main types of Wechsler intelligence tests:

Wechsler Pre-school and Primary Scale of Intelligence (WPPSI) - 3-7 years

Wechsler Intelligence scale for Children (WISC) - 7-16 years

Wechsler Adult Intelligence Scale (WAIS) - 16 years and over

The first was the Wechsler-Bellevue Intelligence Scale (Wechsler, 1939).

Replaced 1955 by the Wechsler Adult Intelligence Scale (WAIS).

1981 revision is referred to as the WAIS-R.

A subsequent revision was conducted in the US in 1997 and the presentscale is the 3rd edition, known as the WAIS-III. The revised version hasalmost 80 per cent of the original form. A number of improvements have been made including an attempt to make it more culturally fair.

The WAIS(R) was standardised on a sample of 1,800 U.S. subjects, ranging from 16 to 74 years of age. It was a highly stratified sample, broken down into 9 different age groups. Equal numbers of men and women were used, as were white and non•white subjects, in line with census figures. It was further broken down into four geographic U.S. regions and six occupational categories. There was also an attempt to balance urban and rural subjects. The mean I.Q. for each age group on this test is 100, with a standard deviation of 15. The WAIS scales have

impressive reliability and validity.

There are different adaptations of the scale by country. For example, inAustralia we have the Australian adaptation of the WAIS-R (1989).

11 separate subtests, which are broken into the Verbal scale (6 subtests) and the Performance scale (5 subtests).

A person taking the test receives a full-scale IQ score, a verbal IQ score, a performance IQ score, as well as scaled scores on each of the subtests.

WAIS Scales

Verbal WAIS scales

1. Information: 29 questions - a measure of general knowledge.

2. Digit Span: Subjects are given sets of digits to repeat initially forwards then backwards. This is a test of immediate auditory recall and freedom from distraction.

3. Vocabulary: Define 35 words. A measure of expressive word knowledge. It correlates very highly with Full Scale IQ

4. Arithmetic: 14 mental arithmetic brief story type problems. tests distractibility as well as numerical reasoning.

5. Comprehension: 16 questions which focus on issues of social awareness.

6. Similarities: A measure of concept formation. Subjects are asked to say how two seemingly dissimilar items might in fact be similar.

Performance WAIS scales

7. Picture Completion: 20 small pictures that all have one vital detail missing. A test of attention to fine detail.

8. Picture Arrangement: 10 sets of small pictures, where the subject is required to arrange them into a logical sequence.

9. Block Design: Involves putting sets of blocks together to match patternson cards.

10. Digit Symbol: Involves copying a coding pattern.

11. Object Assembly: Four small jig-saw type puzzles.

Interpretation of the WAIS (R)

Three IQ scores are obtained from the WAIS(R):

1. Verbal IQ2. Performance IQ3. Full Scale IQ

Interpretation is fairly systematic and can be broken down into a number of discrete steps:

1. Obtain the 3 IQ scores. What standardized categories do they fall into?2. Is there a Verbal-Performance discrepancy? Is it significant?3. Break WAIS scores down into the factorial sub-structure:

(a) Verbal Comprehension(b) Spatial Perceptual(c) Freedom from Distraction

Are individual sub-tests very low or very high? why?

What is the degree of intra-subtest scatter?

Discussion question

Do you believe that this type of test is tapping "intelligence"

More detailed notes about the WAIS-R

“Intelligence is multifaceted as well as multidetermined…What it always calls for is not a particular ability but an overall competency or global capacity” (1981, p. 8). So speaks David Wechsler writing in 1981. The WAIS-R is an individual test of intelligence, was a revision of the original Wechsler-Bellvue Scale created in 1939 and updated in 1955. This revision has subsequently been updated in 1997 but I’lltalk about this one as it’s the one referred to in tutes this week and is very similar to the 1997 revision.

According to Wechsler, intelligence is influenced by personality traits and other nonintellective components, such as anxiety, persistence and goal awareness. These nonintellective factors are important, according to Wechsler, but he remarks”no amount of drive will develop a dullard into a mathematician” (1981, p.8).

The WAIS-R gives a global IQ and also two separate IQ’s for the two scales: verbal and performance. There are 6 verbal subscales and 5 performance subscales.Wechsler believes that this test is a good measure of “g”. The two scales can be used separately to see if a person has particular strengths or weaknesses.Wechsler suggests that if there is more than 15 IQ points difference between thetwo main scales then this might be cause for further investigation. The design ofthe test, with the two scales, means that the verbal & performance scales can be

used alone. The Performance section alone can be used with examinees who are unable to properly comprehend or manage language, or the Verbal scale alone canbe used with examinees who are visually or motor impaired. There is little emphasis on speed in this test with only some subscales having time limits and some subscales having bonuses for speed.

WAIS-R Psychometrics

So what are some of the psychometric properties of the test? Well firstly a large standardization sample was used of 1880 Americans. This sample was 50% male and 50% female. The individuals who formed the standardization sample were aged from 16 years 0 months to 74 years 11 months. The standardization samplewas highly representative of the US population in terms of age, sex, race, geographic region, occupation, education and urban-rural residence. The individuals in the standardization sample were tested between Nay 1975 and May 1980 at 115 testing centres across the U.S.

The scaled scores were based on a reference group of 500 subjects in the standardization sample aged between 20 and 34. Although scaled scores for each of the 11 subtests are obtained using a single table based on the reference group, IQs are derived separately for each of the age groups (there are nine e.g. 16-17, 18-19, 20-24, 25-34….70-74).

The test can be used for people aged 16 and up. It has found to be appropriate foruse with those over 74.

So the WAIS has a good standardization sample and it is also considered to be reliable and valid.

The reliability coefficients: (internal consistency) are .93 for the Performance IQ averaged across all age groups and .97 for the Verbal IQ, with an r of .97 for the full scale. Reliability for the 11 substests is not as strong.

Split half reliability: .95+ (very strong)

Evidence supports the validity of test as a measure of global intelligence. It does seem to measure what it intends to measure. It is correlated highly with other IQ tests (e.g. The Stanford-Binet), it correlates highly with empirical judgements of intelligence; it is significantly correlated with a number of criteria of academic and life success, including college grades, measures of work performance and occupational level. There are also significant correlations with measures of institutional progress among the mentally retarded.

One concern we discussed in some of my tutorials was with reference to the comprehension subscale on the Verbal Scale. Was a question such as “What is the thing to do if you find an envelope in the street that is sealed and addressed and

has a new stamp?” a valid measure of intelligence. The only fully correct responseto that question (i.e. score of 2 is if you mail it or return it the post-office or a postman. You get one point if you recognise it belongs to someone else and try togive it to say a policeman and you get 0 points if you suggest opening it, which frankly is not morally correct in our society but may be a clever thing to do especially if you see some cash in it! So it’s a culturally and morally loaded question. The topic of culture-fair tests is a topic we’ll consider in the tutes this week.

Inroduction to individual differences - An undergraduate psychology course in individual differences

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Individual DifferencesIntroduction to Individual DifferencesLast updated:

Individual differences is a cornerstone subject area in modern psychology. In many ways, it is the "classic" psychology that the general public refers to - it refers the psychology of the person - the psychological differences between people and their similarities.

Plato stated more than 2000 years ago:

“No two persons are born exactly alike; but each differs from the other in natural endowments, one being suited for one occupation and the other for another.”

Individual difference psychology examines how people are similar and how theydiffer in their thinking, feeling and behaviour. No two people are alike, yet no two people are unlike. So, in the study of individual differences we strive to understand ways in which people are psychologically similar and particularly what psychological characteristics vary between people.

In the Western psychology approach to individual differences, it is generally assumed that:

People vary on a range of psychological attributes It is possible to measure and study these individual differences individual differences are useful for explaining and predicting

behaviour and performance

We can classify people psychologically, according to their intelligence and personality characteristics, for example, with moderate success, however people are complex and much is still left unexplained. There are multiple and often conflicting theories and evidence about individual difference psychology.

Human beings have been aware of individual differences throughout history, e.g.

Gender differences -hunters=men, gatherers=women Intelligence differences - caste, class, education, etc. Personality differences - job specialisations

Early study of individual differences

We have come a long way since Franz Gall invented phrenology in the early 1800s. Phrenology is the study of an individual's bumps on the skull, which

02 Aug 2005

supposedly reveal character traits and mental abilities.

Phrenology had such vogue that by 1832 there were 29 phrenological societies in Britain and many journals in both the UK and US devoted to the study of phrenology. It was seriously proposed to select Members of Parliament from their "bumps". Some phrenologists even moulded children's heads to accentuate good qualities and minimise bad ones!

Despite the theory being incorrect one of its assumptions holds true: the idea that various brain regions have particular functions.

Darwin suggested that nature selects successful traits through the “survival of the fittest”. His cousin, Sir Francis Galton (1822-1911) concluded that he could apply the principle scientifically. Why not measure human traits and then selectively breed superior people? He assumed human traits, everything from height and beauty to intelligence and ability, to personality traits such as even- temperedness, were inherited.

Modern psychology has formalised the study of individual differences over the last 100 years. Individual differences psychology is still a young science and a relatively recent development in modern psychology. There are still many debates and issues. Current knowledge will change and evolve. So, have an open-minded, but critical perspective as we go along!

Since there are multiple and controversial viewpoints, it is necessary to move beyond reliance on personally preferred viewpoints to also embrace alternative perspectives, particularly those which are utilized in psychological practice and which have solid research support.

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Why study intelligence?

Intelligence Why Study Intelligence? Last updated:30 Jul 2005

Why study intelligence?

Humans are unique in their intelligence. Intelligence is arguably the most significant individual difference. The study of intelligence is historically central to modern psychology. Intelligence

theory and testing has played a very important role in the history and evolution of modern psychology.

Intelligence is widely measured & used in decision making, e.g. clinical, education,job selection, etc.

Intelligence arguably underlies all other aspects of human psychology. Intelligence is a ubiquitous psychological difference between people which is often

overlooked. Intelligence has been considered as a 6th personality factor to be added to the "Big 5"

personality factors. Intelligence theory and testing has had a checkered history which illustrates important

ethical issues in science and psychology.

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What do you Think about Intelligence?

What do you Think about Last updated:In

en

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30 Jul 2005

What do you Think about Intelligence?

What is your definition of intelligence? What are the names of some psychologists who have studied

intelligence? What would you like to know about intelligence?

What is intelligence? Many definitions...

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Intelligence

What is Intelligence?...Many definitions

Last updated: 30 Jul 2005

A proposed definition of intelligence

Intelligence is:

a ubiquitous individual difference a hypothetical construct reflected in a variety of behaviours which demonstrate a cognitive capacity

for: thinking and reasoning learning and adapting

Also see - Student definitions of intelligence

Classic definitions of intelligence

"The ability to carry out abstract thinking." (Terman, 1921)

"The capacity for knowledge, and knowledge possessed." (Henmon, 1921)

"The capacity to learn or to profit by experience."(Dearborn, 1921)

"The capacity to acquire capacity."(Woodrow, 1921)

"Intelligence is what is measured by intelligence tests." (Boring, 1923)

"A global concept that involves an individual's ability to act purposefully, thinkrationally, and deal effectively with the environment."(Wechsler, 1958)

"Intelligence is a general factor that runs through all types of performance." (Jensen)

"A person possesses intelligence insofar as he had learned, or can learn, to adjusthimself to his environment."(Colvin, cited in Sternberg, 1982, p.30)

"Intelligence is adaption to the environment."(unknown)

"Intelligence is that faculty of mind by which order is perceived in a situationpreviously considered disordered."

(R.W. Young, cited in Kurzweil, 1999) "Intelligent activity consists of grasping the essentials in a given situation

and responding appropriately to them."(unknown)

"Intelligence is the ability to use optimally limited resources - including time - toachieve goals."(Kurzweil, 1999)

"Intelligence is what you do when you don't know what to do." (unknown)

"Intelligence is a hypothetical idea which we have defined as being reflected by certain types of behaviour."(unknown)

Key players in the history & development of intelligence & testing

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Intelligence

Key Players in the History & Development of Intelligence &Testing

Last updated: 30 Jul 2005

1. Francis Galton: The 1st Modern Attempt (late 1800s)

2. Alfred Binet: The origins of IQ Testing (early 1900’s)

3 & 4. Terman (1916) and Stern (1912) 5. Yerkes: Army Tests (WWI)

6. Charles Spearman: “g” (1920’s)

7. Weschler: Intelligence Scales for Adults and Children (1939

-present) 8. Thurstone: Primary Mental Abilities (1930’s)

9. Cattell: Fluid & Crystallised Intelligence (1960’s)

10. Guilford: many, many factors! (1960’s - present)

11 & 12. Vernon & Carroll: Hierarchical Approaches (1960’s

-present) 13. Howard Gardner: Multiple intelligences (1980s to the

present) 14. Robert Sternberg (1970s to present)

References

This is an overview of key players in the modern history of intelligence testing – many of whom you may already be familiar with from their work on other aspects of psychology.

1. Francis Galton: The 1st Modern Attempt (late 1800s)

Intelligence tests are grounded in the work of Francis Galton in the late 19th century. Galton is considered to be the father of the study of individual differences [and, incidentally was the half-cousin of Charles Darwin]. For Galton, measurement of intelligence was to be as direct as possible a measure of underlying intelligence. Hence, Galton suggested reaction time as a feasible approach and pursued various sensori-motor measurements.

Interestingly, more contemporary "Galton-like" approaches are being pursued by psychologists such as Arthur Jensen and Mike Andersen who assert that they are assessing theintegrity of the central nervous system - inherent capabilities (Intelligence A) - as opposed to manifestations of intelligence in everyday life (Intelligence B). (Weinberg, 1989).

2. Alfred Binet: The origins of IQ Testing (early 1900’s)

Alfred Binet is celebrated in history as the man who created the first 'intelligence test' in the form as we know them today. He is commonly known as the “father” of IQ testing.In 1904, Binet was commissioned by the French Ministry of Public Instruction to developtechniques for identifying primary grade children whose lack of success in normal classrooms suggested the need for some form of special education (Gould, 1981).In 1905 he produced the Binet-Simon scale [with Theodore Simon] - the first intelligence test. Binet took a pragmatic approach, choosing a series of 30 short tasks related to everyday problems of life (e.g.attend to simple instructions

name parts of the body compare lengths and weights counting coins, assessing which of several faces is 'prettier', naming objects in a picture, digit span (the number of digits a person can recall after being shown a long list), word definition filling in the missing words in sentences, etc.

Supposedly all these tasks involved basic processes of reasoning.

The tests were arranged so as to be of increasing difficulty. Each level of tests matched a specific developmental level - i.e. all tests at a given level were capable of being solved by any normal child in that specific age-group.

This was a turning point in psychology: A new type of test had been produced in which the average level of performance was the criterion. In 1908 the test was revised and then again in 1911. This edition was the model for many future tests. The test results proved to becorrelated with other criteria (e.g. results of school examinations, assessments of teachers, etc.)

3 & 4. Terman (1916) and Stern (1912)

Lewis Terman (1877-1956) of Stanford University in the US decided to use Binet's test. He found that the Paris-developed age norms didn't work very well for Californian school children. So he revised the test: adapted some items, added other items, established new age norms, and extended the upper age limit to "superior adults". This became the Stanford-Binetrevision in 1916. In this revision the Intelligence quotient first appeared. The IntelligenceQuotient or IQ was a score meant to quantify intellectual functioning to allow comparison among individuals. To arrive at an IQ score, Terman relied on a formula expressing the relation between an individual’s mental age and chronological age developed in 1912 in Germany by Wilhelm Stern: 1912 Wilhelm Stern proposed the following formula:

IQ = mental age x 100 chronological age

This formula works fairly well for children but not for adults (Thomson, 1968; Weinberg, 1989)

5. Yerkes: Army Tests (WWI)

The US army at the beginning of WWI was faced with the problem of assessing the intelligence of great numbers of recruits in order to screen, classify, and assign them to suitable tasks. The Stanford-Binet test required a highly trained person for individual administration - thus it would prove time consuming and costly for large-scale use.

So, when the US entered WWI in 1917 a committee was appointed by the APA to consider ways that psychology might assist the conduct of the war. Head of this committee was Robert Yerkes. His brief was to develop group intelligence testing.

Robert Yerkes, a psychologist and army major, assembled a staff of 40 psychologists [including Terman] to develop a group intelligence test. This resulted in the Army Alpha and Army Beta tests. The Beta was a version of the Alpha specifically for use with non-English- speaking and illiterate persons. [Instructions to those taking the Beta were given by demonstration or pantomime, rather than orally or in writing.]

In the end, over a million people were tested, but not until late in the war. Thus the work actually had little effect on the war, but did a great deal to enhance the status of psychology. After the war, industry, business and education saw potential value of psychological testing

Note that the validity of the Beta test, in particular, has since been questioned rather damningly by Gould (1981).

6. Charles Spearman: “g” (1920’s)

Up to now, the approaches to intelligence had been very pragmatic - i.e. tests were developed for particular needs. However, another approach to understanding intelligence, involved analysing data that was already collected.

Charles Spearman (1927) analysed the relations among experimental intelligence tests using 'factor analysis'. He argued that, as a rule, people who do well on some intelligence tests also do well on a variety of intellectual tasks [vocabulary and mathematical and spatial abilities]. And if people did poorly on an intelligence test, then they also tended to do poorly on other intellectual tests. That is, he observed correlations among performance on a variety of intellectual tasks.

Thus, he proposed, a 'two-factor' theory of intelligence:

- General Ability (g): which was required for performance of mental tests of all kinds; hecalled this a kind of 'mental energy' that underlies the specific factors- Special Abilities: which were required for performance on just one kind of mental test.- e.g. Scores on a verbal comprehension test are largely determined by one’s level of generalintelligence but they are also affected by one’s specific ability to perform verbal comprehension tasks.

But the main thrust of Spearman's analysis was this idea of a general intellectual capacity. This formed a major theoretical platform for many subsequent approaches to intelligence.

It might be also noted, however, that Spearman was perhaps excessively enthusiastic about g. For example, he advocated restricting voting rights to people whose g exceeded a certain level, and he was a eugenicist (eugenics comes from the Greek "eugenes" meaning well-born)- arguing that only people with a certain level of g should be allowed to have offspring.

"g" was controversial then as now.

7. Weschler: Intelligence Scales for Adults and Children(1939 - present)

Another test designer was David Wechsler. Wechsler felt that the Binet scales were too verbally loaded for use with adults, so he designed an instrument with sub-tests to measure both verbal and nonverbal abilities, largely borrowing from many other tests, such as the US Army Alpha test. He adopted a mean score of 100, since the Stanford-Binet metric had become universally accepted. The original Weschsler-Bellevue test in 1939 proved quite successful in civilian and military applications.

In 1949, Wechsler produced the Wechsler Intelligence Scale for Children (WISC), which competed with the Stanford-Binet test.In 1955, he produced a revision of the adult scales named the Wechsler Adult Intelligence Scale (WAIS). And later he produced a scale which could be used with pre-primary children. These scales have all been revised, but still show a distinct resemblance to the original 1939 scale.

8. Thurstone: Primary Mental Abilities (1930’s)

Another 'factor analyst', Thurstone (1938), accepted Spearman's hypothesis of a general factor. But he disputed its importance. He argued that g is in fact a second order factor or phenomenon - one which arises only because the primary or 'first-order' factors are related to one another. Thus, Thurstone identified 7 'primary mental abilities' which he judged to be

Key players in the history & development of intelligence & testing

more important. These were:

1.Verbal Comprehension: vocabulary, reading, comprehension, verbal analogies, etc.2. Word fluency: the ability to quickly generate and manipulate a large number of words withspecific characteristics, as in anagrams or rhyming tests3. Number: the ability to quickly and accurately carry out mathematical operations4. Space: spatial visualizations as well as ability to mentally transform spatial figures5. Associative Memory: rote memory6. Perceptual Speed: quickness in perceiving visual details, anomalies, similarities, etc.7. Reasoning: skill in a variety of inductive, deductive, and arithmetic reasoning

tasks So, Thurstone's approach constituted the first multi-factor approach to

intelligence.

Thurstone's tests have largely dropped out of use because the hope that they would be able tomore accurately predict academic or occupational performance than general intelligence wasnot fulfilled.

Nevertheless, the main argument and findings are important: that intelligence is better described and measured by considering distinct primary mental abilities, rather than a singlefactor g which does not provide specific information about specific intelligences.(see Flanagan, Genshaft & Harrison, 1997; Murphy & Davidshofer, 1998).

9. Raymond Cattell: Fluid & Crystallised Intelligence(1960’s)

Raymond Cattell (1963) [not to be confused with James McKeen Cattell, a contemporary of Galton's who was also significantly involved in early attempts at psychological measurement]suggested that there are two related but distinct components of g: fluid and crystallised intelligence.

Fluid: ability to see relationships, as in analogies and letter and number series = primary reasoning ability

Crystallised: acquired knowledge and skills = factual knowledge

Fluid intelligence decreases with age and crystallised intelligence increases with age. Thus mathematicians and scientists, who need fluid intelligence, produce their best work in thier 20s and 30s; whereas those in the field of history, philosophy and literature produce their bestwork in their 40s, 50s and beyond as they have accumulated more knowledge. Interestingly, poets, who depend more on fluid than crystallised intelligence, produce their best work earlierthan prose authors: this has been observed in all cultures, languages and throughout history.

10. Guilford: many, many factors! (1960’s - present)

Guilford (1967; 1988) parted company from the majority of factorial theorists by refusing toacknowledge the existence of any general factor at all. Instead, he proposed that intelligencecomprises 180 elementary abilities. The 180 elementary abilities are made up of a combination of three dimensions which he calls:- operations: what a person does (6-types)- contents: the material on which operations are performed (5-types)- products: the form in which the information is stored and processes (6-types).Guilford proposed that each combination of a specific operation, a specific type ofcontent and a specific type of product defines a unique type of intelligence (6x5x6 = 180).In later versions of his theory he proposed even more types of intelligence.

Due largely to the practical implications of such a model, Guilford's theory has not significantly influenced psychological testing of intelligence.

11 & 12. Vernon & Carroll: Hierarchical Approaches (1960’s - present)

Probably the most widely accepted factorial description of intelligence is a hierarchical one, e.g. Vernon (1960, 1965, 1971) and Carroll (1993). Vernon accepted, in a sense, that both Spearman (single g factor) and Thurstone (multiple primary mental abilities) were right. Vernon suggested that intelligence can be described as comprising abilities at varying levels of generality:- at the highest level of generality (i.e. top of the hierarchy) is g as defined by Spearman);- at the next level are 'major group' factors, such as:- verbal-educational ability [the kind of ability needed for successful performance in courses such as English, history, and social studies] and- practical-mechanical ability [the kind of ability needed successful performance in courses such as draughtsmanship and car mechanics];- at the next level are 'minor group' factors, which can obtained by subdividing the major group factors;- and at the lowest (the bottom of the hierarchy) are specific factors again of the kind identified by Spearman.

So, Vernon inserted 2 further levels between Spearman's g and specific factors relevant to only one test.

Carroll (1993) proposed the three-stratum model of cognitive ability (similar to Vernon's).

These hierarchical descriptions of intelligence may be viewed as filling in the gaps between the extreme approaches of Spearman and Thurstone.

13. Howard Gardner: Multiple intelligences (1980s to thepresent)

Howard Gardner (1983; 1993) supports Thurstone’s notion that intelligence comes in different packages. The most widely cited version of Gardner’s concept of intelligence is thatthere are seven different types of intelligence. Gardner has played around with this number and suggested a possible one or two more or even (in 1999) the possibility of a smaller number of intelligences. He argues that the seven intelligences are: verbal, mathematical,musical, spatial, kinaesthetic, interpersonal (social skills) and intrapersonal (self- understanding) functioning. He argues that these different intelligences are independent of one another. Critics argue: not all these things are intelligence: More next week.

14. Robert Sternberg (1970s to present)

Robert Sternberg (1977, 1985) together with his colleague Richard Wagner (1993, 1995) argues that there are three intelligences:

Academic Practical Creative

Sternberg and Wagner have designed a test of practical intelligence.

References

History of the influences in the development of intelligence theory & testing

Sternberg's Triarchic Theory of Intelligence

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Individual DifferencesSternberg's Triarchic Theory of Last updated:Intelligence Intelligence 24 Jan 2004

Overview of Sternberg's Triarchic Theory of Intelligence

Analytic (componential) Facet or Subtheory

Creative (experiential Facet or Subtheory

Practical (contextual) Facet or Subtheory

Sternberg: Why intelligent people fail

Overview of Sternberg's Triarchic Theory of Intelligence

Sternberg's Triarchic Theory of Human Intelligence (1977, 1985, 1995) subsumes both Spearman’s g and underlying information processing components. His triarchic theory includes three facets or subtheories:

Analytical (componential) Creative (experiential) Practical (contextual)

Sternberg's theory builds on his earlier componential approach to reasoning. Histheory is mostly based on observing Yale graduate students. Sternberg believes that if intelligence is properly defined & measured it will translate to real-life success.

Sternberg's Triarchic Theory is an important effort to synthesize the various theories of intelligence.

Analytical (componential) Facet (or Subtheory)

Analytical Intelligence similar to the standard psychometric definition of intelligence e.g. as measured by Academic problem solving: analogies and puzzles, and corresponds to his earlier componential intelligence. Sternberg considers this reflects how an individual relates to his internal world.

Sternberg believes that Analytical Intelligence (Academic problem-solving skills)is based on the joint operations of metacomponents and performance components and knowledge acquisition components of intelligence

Metacomponents: control, monitor and evaluate cognitive processing. These arethe executive functions to order and organise performance and knowledge acquisition components. They are the higher-order processes that order and organise the performance components. Used to analyze problems and pick a strategy for solving them. They decide what to do and the performance components actually do it.

Performance Components: execute strategies assembled by the metacomponents. They are the basic operations involved in any cognitive act. They are the cognitive processes that enable us to encode stimuli, hold information in short-term memory, make calculations, perform mental calculations, mentally compare different stimuli, retrieve information from long- term memory.

Knowledge acquisition components: are the processes used in gaining and storing new knowledge - i.e. capacity for learning. The strategies you use to help memorize things exemplify the processes that fall into this category.

Sternberg feels that IDs in intelligence are related to IDs in the use of these cognitive processes. He feels that people with better reasoning ability generally spend more time understanding the problem but reach their solution faster thanthose who are less skilled at the task.

Creative (experiential) Facet (or Subtheory)

Creative Intelligence: this involves insights, synthesis and the ability to react to novel situations and stimuli. This he considers the Experiential aspect of intelligence and reflects how an individual connects the internal world to external reality.

Sternberg considers the Creative facet to consist of the ability which allows people to think creatively and that which allows people to adjust creatively and effectively to new situations.

Sternberg believes that more intelligent individuals will also move from

consciously learning in a novel situation to automating the new learning so that they can attend to other tasks.

Two-Facet Subtheory (Novelty & Automatization)

Basic assumption: That there are two broad classes of abilities associated withintelligence: novelty skills and automatization skills. A task measures intelligence if it requires the ability to deal with novel demands or the ability toautomatize information processing (two ends of a continuum).

Novel tasks or situations are good measures of intellectual ability because they assess an individual's ability to apply existing knowledge to new problems.

Practical (contextual) Facet (or Subtheory)

Practical Intelligence: this involves the ability to grasp, understand and dealwith everyday tasks. This is the Contextual aspect of intelligence and reflectshow the individual relates to the external world about him or her.

Sternberg states that Intelligence is: "Purposive adaptation to, shaping of, and selection of real-world environments relevant to one's life" (Sternberg, 1984, p.271)

Purposive means that intelligence is directed towards goals, however vague or subconscious they may be. This means that intelligence is indicated by one's attempts to adapt to one's environment.

Practical Intelligence can be said to be intelligence that operates in the real world. People with this type of intelligence can adapt to, or shape their environment. It might also be called “Street-smarts”. In measuring this facet, not only mental skills but attitudes and emotional factors that can influence intelligence are measured.

So this practical intelligence is a combination of:

(a) adaptation to the environment in order to have goals met(b) changing the environment in order to have goals met(c) or, if (a) and (b) don't work moving to a new environment inwhich goals can be met

Sternberg believes that individuals considered intelligent in one culture may be looked on as unintelligent in another.

An important asset of this theory is to avoid defining intelligence in terms of

intelligence tests rather than performance in the everyday world (which is, after all, what intelligence tests try to predict!).

Measuring practical intelligence:

Sternberg Multidimensional Abilities Test measures all 3 intelligences, on separate scales

Sternberg and Wagner’s test of Practical Managerial Intelligence measures: ability to write effective memos ability to motivate people knowledge of when to delegate ability to “read” people

When measuring practical intelligence Sternberg looks at things such as how people decode nonverbal messages e.g. can you tell who are the real couples?

Intelligence as Speed of Processing

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Individual Differences

Intelligence Intelligence as Speed of ProcessingLast updated:

Speed of Processing Theory

Are intelligent people faster at processing information?

Mike Anderson: Speed of Processing

Speed of Processing Theory

“Faster cognitive processing may allow more information to be acquired” (Vernon, 1983).

This theory of intelligence is in many ways, a modern equivalent of Francis Galton's attempt (and others such as Jensen since) who tried to measure reaction time as a way of getting an indication of how fast the brain is working.

Galton stated that “Synaptic efficiency can explain why one individual is more intelligent than another”. We commonly use the term “slow”, for example, to describe people who perform poorly at school, or "quick" to describe those who are efficient at solving mental problems.

In more modern terms, the basic premise is that the speed at which we process thought can explain why one individual is more intelligent than another.

Are intelligent people faster at retrieving and processing information?

So, are intelligent people faster at retrieving and processing information?

Evidence for these 'low-level' theories of intelligence come from the correlations between IQ and:

inspection time: speed of intake of perceptual (stimulus). For example, the time taken to discriminate reliably between two lines of similar length. (Deary & Stough, 1996). Lot of work done by Deary in this areaand he claims high correlations between inspection time and IQ (around0.4 )

Reaction time: individuals who have a quick reaction time are those who can process information quickly. The idea is that slow processing of information leads to an incapacity to handle complex information. Again

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there is some support for this notion.

Evoked potentials: with more intelligent people, their brain waves register a simpl stimulus more quickly and with greater complexity (Caryl, 1994) and their evoked brain response is faster when they perform a simple task.

Mike Anderson: Speed of Processing

Mike Anderson is an eminent researcher in the area of intelligence (he’s an Australian based at the University of Western Australia in Perth). He’s posited a theory of Minimal Cognitive Architecture (1992, 1999) in which he suggests thatone route to knowledge is through thinking, and thought is constrained by thespeed of some basic processing mechanism and it is this speed that is the fount of one's general intelligence or IQ.

According to Anderson, this speed of processing is an innate component of individual differences. Anderson (1992) however also argues that there is moreto intelligence than speed of processing (p. 13). It is also to do with higher levels of knowledge which are acquired through the low-level components (such as processing speed). In other words this low-level functioning limits the higher level capacities.

Further to this, Anderson proposes that it is specificity and individual differencesin types of knowledge which subsequently leads to the specific abilities such as those identified by Gardener.

Gardener's Multiple Intelligences

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Individual Differences

Intelligence Gardener's Multiple IntelligencesLast updated:

Overview of Gardener's Multiple Intelligences

Gardener's Approach to Intelligence

Gardener's Five Signs of an Intelligence

Gardener's Seven Intelligences

Strengths of Gardener's Multiple Intelligence Theory

Weaknesses of Gardener's Multiple Intelligence Theory

More about Gardener's Multiple Intelligences...

Overview of Gardener's Multiple Intelligences

Gardner continues in the tradition of Thurstone's proposal that there is no g (general intelligence) but rather multiple, distinct intelligences. Gardener proposes seven intelligences (although he does not limit the possible number)

1. Linguistic intelligence2. Musical intelligence3. Logical- mathematical intelligence4. Spatial intelligence5. Bodily-Kinaesthetic intelligence6. Interpersonal intelligence7. Interpersonal intelligence

Additional 'candidate' intelligences

are:

Naturalistic intelligence (ability to discern patterns in nature - e.g. Darwin) Spiritual Intelligence - recognition of the spiritual Existential intelligence - concern with 'ultimate issues'

Gardener's approach to intelligence

Howard Gardner (1983, 1993, 1999) believes that we have multiple intelligences, rather than a general intelligence that underlies performance in alltasks (g).

In arguing that there are distinct and separate components to intelligence

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Gardener offers nothing particularly new. However, what is new about Gardner's work is that he does not attempt to support his approach purely through statistical reanalysis of data (e.g. as Thurstone did), but instead he haslooked at various "signs" to inform his theory of what constitutes intelligence.

Gardener's multiple intelligence theory is supported by the current anti-g Zeitgeist. He also suggests that different cultures highlight certain intelligences& minimize others.

Gardener's Five Signs of an Intelligence

Gardener has examined a variety of sources in order to formulate his theory ofintelligence: intelligence tests, cognition experiments, neuropsychological research, child prodigies and idiot savantes.

As a result, Gardener has proposed five "signs" or criteria that he uses to identify whether an intelligence qualifies as being distinct and autonomous from other intelligences:

1. Neuropsychological evidence: isolation by brain damage:

One criterion was whether an intelligence could be isolated neuropsychologically. Gardner argues that people have multiple intelligences because they have multiple neural modules. Each module, he believes, has its own way of operating and its own memory systems. Brain damage may sometimes impair one intellectual skill whilst other skills remain at least partially intact afterbrain damage. For example, brain-injured musicians may have impaired speech, yet retain the ability to play music (aphasia withoutamusia (Hodges, 1996; Sergent, 1993).

2. The existence of individuals with exceptional talent:

Selective competence (such as idiot savants, prodigies), like selective deficits, suggests autonomy of that particular competence. In other words, the presence of extraordinary intelligence in one areasuggests a distinct form of intelligence. If Mozart could write music before he could even read, then the neural systems involved in musical intelligence must be separate from those involved in language processing.

3. A distinct developmental history:

Another source of evidence for an intelligence is a characteristic

developmental trajectory leading from basic and universal manifestations to one or more expert end-states. For example, spoken language develops quickly and to great competence in normal people. In contrast, while all normal individuals can count small quantities, few progress to an understanding of higher mathematics even with formal schooling. (Torff & Gardner, 1999).

4. Experimental evidence:

e.g. individuals performing two different tasks at once indicate that some intelligences (or is it just abilities) operate autonomously.

5. Psychometric support:

e.g. factor analysis shows different factors in intelligence. FA generally supports the existence of two big group factors: verbal and spatial (Torff & Gardner, 1999).

Gardener's Seven Intelligences

Gardener concludes that the cumulative evidence points to seven (or possibly eight) distinct intelligences. The first three are somewhat similar to previous components of intelligence identified by other approaches; whereas the secondfour/five are more novel. He believes these develop differently in different people due to both heredity and training. He believes that all need to be measured to provide a truly global assessment of intelligence.

1. Linguistic Intelligence: involved in reading, writing, listening and talking2. Logical-Mathematic Intelligence: involved in solving logical

puzzles, deriving proofs, performing calculations3. Spatial Intelligence: involved in moving from one location to

another or determining one's orientation in space4. Musical Intelligence: involved in playing, composing, singing and

conducting. Furthermore, Gardner believes that auto mechanics andcardiologists may have this kind of intelligence in abundance as they make diagnoses on the careful listening to patterns of sounds.

5. Bodily-Kinaesthetic Intelligence: involved in using one's body (or parts of it) to perform skilful and purposeful movements (dancers, athletes and surgeons)

6. Intrapersonal Intelligence: involved in understanding oneself and having insight into one's own thoughts, actions and emotions (self- understanding).

7. Interpersonal functioning: involved in understanding of othersand one's relations to others. Being high in social skills(psychologists, teachers and politicians are supposed to be highin this type of

intelligence).8. The eighth intelligence was proposed by Gardner in 1999 and he

calls it Naturalistic Intelligence. This intelligence involves the ability to understand and work effectively in the natural world. This is exemplified by biologists and zoologists.

Strengths of Gardner's Multiple Intelligence Theory

helps to explain the variety of individual differences in different types of mental performance

based in developmental, clinical, case study and educational evidence

Criticisms of Gardener's Multiple Intelligence Theory

narrow intelligences may meet criteria, e.g. 20 to 30 intelligences may also have been convincing

are these intelligences or just 'abilities'? (and what is the difference?) - musical, bodily-kinaesthetic, intra and interpersonal are a source of some controversy

doesn't explain why some people are more intelligent than others these 'intelligences' are not all essential for successful adaptation (one

of the common definitions of intelligence) ultimately there is not really much HARD scientific evidence.

Psychological Testings Versus Psychological Assessment

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Individual DifferencesPsychological Testing versus Last updated:Intelligence Psychological Assessment 03 Aug 2003

Assessment is more than testing

Definition of Psychological Testing

Definition of Psychological Assessment

Assessment is more than testing

Psychological testing (e.g., an intelligence test, personality test, or mental health test) occurs as part of the process of psychological assessment. Professional psychological assessment usually also includes:

interview demographic information medical information personal history observations by others

Thus, the results of a psychological test are rarely used on their own.

The following definitions should help to clarify the difference between assessment and testing in psychology.

Definition of Psychological Testing

"An objective and standardized measure of a sample of behaviour"

(Anastasi, 1990)

Definition of Psychological Assessment

"An extremely complex process of solving problems (answering questions) in which psychological tests are often used as one of the methods of collecting relevant data"

(Maloney & Ward, 1976)

Essentials of a Good Psychological Test

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Individual Differences

Intelligence Essentials of a Good Psychological Test Last updated:

Reliability - overview

Types of reliability How reliable should tests be?

Validity

Types of validity Sources of invalidity

Generalizability

Standardization

Recommended Links

Reliability - overview

Reliability is the extent to which a test is repeatable and yields consistent scores.

Note: In order to be valid, a test must be reliable; but reliability does not guarantee validity.

All measurement procedures have the potential for error, so the aim is to minimize it. An observed test score is made up of the true score plus measurement error.

The goal of estimating reliability (consistency) is to determine how much of the variability in test scores is due to measurement error and how much is due to variability in true scores.

Measurement errors are essentially random: a person’s test score might not reflect the true score because they were sick, hungover, anxious, in a noisy room, etc.

Reliability can be improved by:

getting repeated measurements using the same test and getting many different measures using slightly different techniques and

methods.

- e.g. Consider university assessment for grades involve several sources. You would not consider one multiple-choice exam question to be a reliable basis for

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testing your knowledge of "individual differences". Many questions are asked in many different formats (e.g., exam, essay, presentation) to help provide a more reliable score.

Types of reliability

There are several types of reliability:

There are a number of ways to ensure that a test is reliable. I’ll mention a few ofthem now:

1. Test-retest reliability

The test-retest method of estimating a test's reliability involves administering the test to the same group of people at least twice. Then the first set of scores is correlated with the second set of scores. Correlations range between 0 (low reliability) and 1 (high reliability) (highly unlikely they will be negative!)

Remember that change might be due to measurement error e.g if you use a tape measure to measure a room on two different days, any differences in the result is likely due to measurement error rather than a change in the room size. However, ifyou measure children’s reading ability in February and the again in June the change is likely due to changes in children’s reading ability. Also the actual experience of taking the test can have an impact (called reactivity). History quiz - look up answers and do better next time. Also might remember original answers.

2. Alternate Forms

Administer Test A to a group and then administer Test B to same group. Correlation between the two scores is the estimate of the test reliability

3. Split Half reliability

Relationship between half the items and the other half.

4. Inter-rater Reliability

Compare scores given by different raters. e.g., for important work in highereducation (e.g., theses), there are multiple markers to help ensure accurateassessment by checking inter-rater reliability

5. Internal consistency

Internal consistence is commonly measured as Cronbach's Alpha (based on inter- item correlations) - between 0 (low) and 1 (high). The greater the number of

similar items, the greater the internal consistency. That’s why you sometimes get very long scales asking a question a myriad of different ways – if you add more items you get a higher cronbach’s. Generally, alpha of .80 is considered as a reasonable benchmark

How reliable should tests be? Some reliability guidelines

.90 = high reliability

.80 = moderate reliability

.70 = low reliability

High reliability is required when (Note: Most standardized tests of intelligence report reliability estimates around .90 (high).

tests are used to make important decisions individuals are sorted into many different categories based upon relatively

small individual differences e.g. intelligence

Lower reliability is acceptable when (Note: For most testing applications, reliability estimates around .70 are usually regarded as low - i.e., 49% consistent variation (.7 to the power of 2).

tests are used for preliminary rather than final decisions tests are used to sort people into a small number of groups based on

gross individual differences e.g. height or sociability /extraversion

Reliability estimates of .80 or higher are typically regarded as moderate to high (approx. 16% of the variability in test scores is attributable to error)

Reliability estimates below .60 are usually regarded as unacceptably low.

Levels of reliability typically reported for different types of tests and measurement devices are reported in Table 7-6: Murphy and Davidshofer (2001, p.142).

Validity

Validity is the extent to which a test measures what it is supposed to measure.

Validity is a subjective judgment made on the basis of experience and empirical indicators.

Validity asks "Is the test measuring what you think it’s measuring?"

For example, we might define "aggression" as an act intended to cause harm to

another person (a conceptual definition) but the operational definition might be seeing:

how many times a child hits a doll how often a child pushes to the front of the queue how many physical scraps he/she gets into in the playground.

Are these valid measures of aggression? i.e., how well does the operational definition match the conceptual definition?

Remember: In order to be valid, a test must be reliable; but reliability does not guarantee validity, i.e. it is possible to have a highly reliable test which is meaningless (invalid).

Note that where validity coefficients are calculated, they will range between 0 (low)to 1 (high)

Types of Validity

Face validity

Face validity is the least important aspect of validity, because validity still needs to be directly checked through other methods. All that face validity means is:

"Does the measure, on the face it, seem to measure what is intended?"

Sometimes researchers try to obscure a measure’s face validity - say, if it’s measuring a socially undesirable characteristic (such as modern racism). But the more practical point is to be suspicious of any measures that purport to measure one thing, but seem to measure something different. e.g., political polls - a politician's current popularity is not necessarily a valid indicator of who is going towin an election.

Construct validity

Construct Validity is the most important kind of validity

If a measure has construct validity it measures what it purports to measure.

Establishing construct validity is a long and complex process.

The various qualities that contribute to construct validity include:

criterion validity (includes predictive and concurrent)

convergent validity discriminant validity

To create a measure with construct validity, first define the domain of interest (i.e.,what is to be measured), then construct measurement items are designed which adequately measure that domain. Then a scientific process of rigorously testing and modifying the measure is undertaken.

Note that in psychological testing there may be a bias towards selecting itemswhich can be objectively written down, etc. rather than other indicators of thedomain of interest (i.e. a source of invalidity)

Criterion validity

Criterion validity consists of concurrent and predictive validity.

Concurrent validity: "Does the measure relate to other manifestations of theconstruct the device is supposed to be measuring?"

Predictive validity: "Does the test predict an individual’s performance inspecific abilities?"

Convergent validity

It is important to know whether this tests returns similar results to other tests which purport to measure the same or related constructs.

Does the measure match with an external 'criterion', e.g. behaviour or another, well-established, test? Does it measure it concurrently and can it predict this “behaviour”?

Observations of dominant behaviour (criterion) can be compared with self-report dominance scores (measure)

Trained interviewer ratings (criterion) can be compared with self-reportdominance scores (measure)

Discriminant validity

Important to show that a measure doesn't measure what it isn't meant to measure- i.e. it discriminates.

For example, discriminant validity would be evidenced by a low correlation betweenbetween a quantitative reasoning test and scores on a reading comprehension test,since reading ability is an irrelevant variable in a test designed to measure quantitative reasoning.

Sources of Invalidity

Unreliability Response sets = psychological orientation or bias towards answering in a

particular way: Acquiescence: tendency to agree, i.e. say "Yes”. Hence use of half -

vely and half +vely worded items (but there can be semantic difficulties with -vely wording)

Social desirability: tendency to portray self in a positive light. Try todesign questions which so that social desirability isn't salient.

Faking bad: Purposely saying 'no' or looking bad if there's a'reward' (e.g. attention, compensation, social welfare, etc.).

Bias Cultural bias: does the psychological construct have the same

meaning from one culture to another; how are the different items interpreted by people from different cultures; actual content (face)validity may be different for different cultures.

Gender bias may also be possible. Test Bias

Bias in measurement occurs when the test makes systematic errors in measuring a particular characteristic or attribute e.g. many say that most IQ tests may well be valid for middle-classwhites but not for blacks or other minorities. In interviews, which are a type of test, research shows that there is a bias in favour of good-looking applicants.

Bias in prediction occurs when the test makes systematic errorsin predicting some outcome (or criterion). It is often suggested that tests used in academic admissions and in personnel selection under-predict the performance of minority applicants Also a test may be useful for predicting the performance of onegroup e.g. males but be less accurate in predicting the performance of females.

Generalizability

Just a brief word on generalizability. Reliability and validity are often discussed separately but sometimes you will see them both referred to as aspects of generalizability. Often we want to know whether the results of a measure or a test used with a particular group can be generalized to other tests or other groups.

So, is the result you get with one test, lets say the WISC III, equivalent to the result you would get using the Stanford-Binet? Do both these test give a similar IQ score? And do the results you get from the people you assessed apply to other kinds of people? Are the results generalizable?

So a test may be reliable and it may be valid but its results may not be generalizable to other tests measuring the same construct nor to populations other

than the one sampled.

Let me give you an example. If I measured the levels of aggression of a very largerandom sample of children in primary schools in the ACT, I may use a scale which is perfectly reliable and a perfectly valid measure of aggression. But would my results be exactly the same had I used another equally valid and reliable measure of aggression? Probably not, as it’s difficult to get a perfect measure of a construct like aggression.

Furthermore, could I then generalize my findings to ALL children in the world, or even in Australia? No. The demographics of the ACT are quite different from those in Australia and my sample is only truly representative of the population of primaryschool children in the ACT. Could I generalize my findings of levels of aggression for all 5-18 year olds in the ACT? No. Because I’ve only measured primary school children and there levels of aggression are not necessarily similar to levels of aggression shown by adolescents.

Standardization

Standardization: Standardized tests are:

administered under uniform conditions. i.e. no matter where, when, bywhom or to whom it is given, the test is administered in a similar way.

scored objectively, i.e. the procedures for scoring the test are specified in detail so that ant number of trained scorers will arrive at the same score forthe same set of responses. So for example, questions that need subjective evaluation (e.g. essay questions) are generally not included in standardizedtests.

designed to measure relative performance. i.e. they are not designed to measure ABSOLUTE ability on a task. In order to measure relative performance, standardized tests are interpreted with reference to a comparable group of people, the standardization, or normative sample. e.g. Highest possible grade in a test is 100. Child scores 60 on a standardized achievement test. You may feel that the child has not demonstrated masteryof the material covered in the test (absolute ability) BUT if the average of the standardization sample was 55 the child has done quite well (RELATIVE performance).

The normative sample should (for hopefully obvious reasons!) be representative of the target population - however this is not always the case, thus norms and the structure of the test would need to interpreted with appropriate caution.

Recommended Links

What are the essentials of a good psychological testing report on an older adult? (American Psychological Association)

Factors influencing internal and external validity (Campbell & Stanley, 1963)

How to choose tools, instruments, & questionnaires for intervention research & evaluation (James Neill, 2004)

Nature vs Nurture in Intelligence

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Individual Differences

Intelligence

Nature vs Nurturein Intelligence

Last updated: 10 Apr 2005

Overview

Nature vs. Nurture - What do you think?

Pendulum of opinion on Nature vs. Nurture through history

Historical trends in the nature-nurture debate

Evidence in favour of “nature”

Evidence in favour of “nurture”

The role of “interaction”

What have we learnt about intelligence?

Final quotes

References

Overview

The issue of what causes individual differences in intelligence goes beyond psychology, and involves moral, political, ethical, educational, social, physiological and statistical issues to name just a few. The issue of how differences in intelligence come about between individuals and groups is a topic of much fascination and controversy - it can arouse strong reactions and elicit personal beliefs and biases.

This page outlines some of the main psychological concepts and evidence that relates to explaining individual differences in intelligence.

As a student, it is your responsibility to develop a familiarity with the basic arguments, strengths, and weaknesses for and against the causal influences and correlates of intelligence.

Nature vs Nurture - What do you think?

In looking for the causes of individual differences in intelligence, a major issue is the relative contribution of genetics and environment.

100%Genetics (Nature)

90%Gen.

80%Gen.

70%Gen.

60%Gen.

50-50

60%Env.

70%Env.

80%Env.

90%Env.

100%Environ. (Nurture)

Rate the extent to which you believe nature and nature influence (cause) human intelligence.

Warning! As you learn more about the theory and research on genetic and environmental influences on human intelligence, you may find that you change some of your beliefs and assumptions.

Pendulum of opinion on Nature vs. Nurture through history

The zeitgeist (the intellectual and culture "flavor" of a time and place) has swung back and forth over time with regard to the amount of influence that nature vs. nature has on human intelligence.

For example, in the late 1800's in the UK, as Darwinism took off, the role of geneticallydetermined capability was considered very important.

This was in constrast, for example, to the 1960's in the USA, when views were more in favor a "tabula rasa" (blank state) view of human intelligence - in other words, all people arecapable of much more, if given conducive environmental conditions in which to reach their potential

Currently the Zeitgeist is the Western psychological world is somewhere inbetween - bothgenetics and environment are seen as playing important roles. To be more precise, the modern view about nature vs nurture in intelligence is "interactionist". This view is well expressed by Ridley (1999, p.77):

"Mother Nature has plainly not entrusted the determination of our intellectual capacities to the blind fate of a gene or genes; she gave us parents, learning, language, culture and education to program ourselves with."

Historical trends in the nature-nurture debate

Late 19th century - early 20th century (Nature)

From the mid to late 1800's through to the early 1900's opinions rested in the nature camp. This was consistent with the scientific discoveries of the role of inheritance and natural selection by Mendel and Darwin.

The major contributor to the psychological argument was Francis Galton in his book "Hereditary Genius: Its Laws and Consequences” (1869).

Galton had observed that the gifted individuals tended to come from families which had othergifted individuals. He went on to analyze biographical dictionaries and encyclopedias, and became convinced that talent in science, the professions, and the arts, ran in families.

Galton took this observation one step further, to argue that it would be "quite practicable toproduce a high gifted race of men by judicious marriages during several consecutive generations".

This suggestion became know as eugenics, "the study of the agencies under social control that may improve or repair the racial qualities of future generations, either physically or mentally." Galton wanted to speed up the process of natural selection, stating that: "What Nature does blindly, slowly, and ruthlessly, man may do providently, quickly, and kindly”.

Galton was convinced that "intelligence must be bred, not trained". Such arguments have had massive social consequences and have been used to support apartheid policies, sterilization programs, and other acts of withholding basic human rights from minority groups.

Post WWI: 1920’s-1930’s

After World War I, careful reanalysis of the mass of intelligence test data took place. This began to challenge the commonly held view that intelligence was directly, genetically linked to racial differences:

e.g. blacks from Illinois had higher IQ scores than whites from 9 southern states - a finding difficult to reconcile with the simple idea that whites are intellectually superiorto blacks.

Evidence now seemed to support a closer link between social class and intelligence, rather than race and intelligence. As a result, a number of psychologists in the 1920s and 1930s shifted their position towards the environmental camp.

The shift against 'nature' views was given momentum by the backlash against the social consequences of government policies:

e.g. sterilization laws had been passed in 24 US States, resulting in 20, 000 people being sterilized against their will. 320, 000 people suffered the same fate in Germany.

1940’s-1990’s

The backlash faded, and the pendulum swung back towards the middle. From the early 1940's, it seemed there was a rejection of simplistic nature or nurture views, with more common recognition of their complex interplay. Nevertheless, social prejudices and inequalities were still evident and growing.

Thus, in the 1960's, the focus of the problem was shifted away from the individual as the cause of the problem, and centered on social determinants. Thhe pendulum swung towards thenurture/environmental end and away from the nature/genetic end. Efforts were made to arrest poor educational achievement through special schooling, and to alleviate poor living conditions through welfare.

It became politically correct to minimize talk and discussion of the role of 'nature' in contributing to any individual differences, let alone intelligence. The evidence of differencesin intelligence between socioeconomic groups and racial groups, however, did not go away.

Recent trends – "The Bell Curve" controversy

From time to time, there have been inflammatory articles which present and interpret evidence of IQ differences between groups (in particular Jensen, 1969). The most recent, and most major of these publications was Herrnstein and Murray's (1994) "The Bell Curve". This book provided momentum to swing the pendulum in the direction of 'nature', at least in the public's eye, but even more so, it generated massive debate and controversy in psychology, sociology, education, and politics, not to mention the media and household. The 800+ page book, written for laypersons, hit the best-seller lists in the U.S.

"The work's main thesis is that an individual's intelligence - no less than 40% and no more than 80% of which is inherited genetically from his or her parents- has more effect than socioeconomic background on future life experiences." Manolakes (1997), p.235

In addition to the premise that measured intelligence (IQ) is largely genetically inherited, a second important premise was that IQ is correlated positively with a variety of measures of

socioeconomic success in society, such as a prestigious job, high annual income, and high educational attainment; and is inversely correlated with criminality and other measures of social failure. It was suggested that SES successes (and failures) are largely genetically caused.

Some sample controversial quotes from "The Bell Curve"

“IQ has more effect on future life experiences than SES” “intervention efforts are largely a waste of time and money” “increasing population of 'lower caste' intelligences, lessening the

nation's 'genetic capital”

Reactions to The Bell Curve:

The Bell Curve" re-ignited the nature-nurture debate. The public debate was (and is) divided.

The politically left saw the authors as "un-American”;- "pseudo-scientific racists”;- and the book as "alien and repellent"

The politically right saw the authors as:- "brave and respectable scholars,”;- whose book was "lucid" and "powerfully written"

The part of The Bell Curve that captured public attention was on the differences in IQbetween African and Caucasian Americans. Further to this were the suggestions madeby Herrnstein and Murray about the implications of a predominantly genetically- inherited intelligence for public and social policy. Since IQ was largely seen as genetically determined, the authors expressed resistance to educational and environmental interventions. They argued that money spent in this way is wasted. Theauthors also argued that America is becoming a society of 'cognitive castes', with the lower caste including a large proportion of African-Americans. Hence their statement that the 'genetic capital' of society is being eroded because the less intelligence, lower class is reproducing at a greater rate than high IQ classes.

Evidence in favour of “nature”

In the heyday of eugenic IQ testing in the 1920s there was no evidence for the heritability of IQ. It was just an assumption of the practitioners. Today that is no longer the case. The heritability of IQ (whatever IQ is!) is now an hypothesis that has been tested - on twins and adoptees. The results really are quite startling. No study of the causes of intelligence has failed to find a certain and often substantial heritability. What varies from study to study is theamount that can be attributed to heritability.

Concordance rates of IQ scores

Evidence from family studies provides the main supporting evidence from whicharguments about the relative roles of genetics and environment are constructed.

A large number of the study of twins reared apart was undertaken by Thomas Bouchard of the University of Minnesota starting in 1979. He “collected” pairs of separated twins from all over the world and reunited them while testing their personalities and IQs. Other studies at the same time concentrated on comparing the IQs of adopted people with those of their adopted parents and their biological parentsor their siblings. Put all these studies together, which include the IQ tests of tens of thousands of individuals, and the table looks like this:

Same person tested twice 87% Identical twins reared together 86% Identical twins reared apart 76% Fraternal twins reared together 55% Biological siblings reared together 47% (studies show that reared apart about 24%) Parents and children living together 40% Parents and children living apart 31% Adopted children living together 0% Unrelated people living apart 0%

Ridley, 1999, p.83 [The number is a percentage correlation . Attach section from Ridley’s book.]

Meta-analytic estimates of the heritability of intelligence

A meta-analysis of 9 family studies was conducted by Daniels, Devlin and Roeder (1997): it included 212 correlations and produced very similar results to those quoted by Matt Ridley. These authors conclude that heritability can account for 48% of the variation in IQ. The highest estimates have come from reviews of research by Herrnstein & Murray, 1994 (74%) and Eysenck (80%). A safer bet is probably to sit on the fence - 50:50!

Heritability indices, however, are not pure measures of genetic inheritance - they included prenatal environmental influences, (e.g. whether the mother smokes, what she eats, etc.) andthe postnatal material environment. Thus these heritability indices are likely to overestimatethe role of genetics.

Correlation of child-parent verbal ability scores

This graph shows correlations between children and their parents and adopted children andtheir biological and adoptive parents on verbal ability scores.

Heritability & intelligence

It must be noted, however, that heritabilty is not pure genetic influence as the pre and postnatal environments must be taken into account. Heritability estimates based on comparing correlations between IQs of monozygotic (identical) twins reared together with IQs of dizygotic (fraternal) twins and siblings are likely to overestimate the genetic component because monozygotic twins share more similar environments - both in the womb and out

twins reared apart are not assigned at random to foster or adoptive parents - sincehomes are selected purposely to with regard to characteristics of the child and characteristics of the family. This would partially account for the IQ correlations attributed to inheritance

twin studies may not be generalizable to the population at large as twins are more susceptible to prenatal trauma leading to retardation. The inclusion of retarded casesmay increase the twin correlation in intellligence test scores.heritability indexes refer to the population on which they were found at the time and is not applicable to an analysis of test performance between two population groups e.g. ethnic groups.

heritability does not indicate the degree to which a trait can be modified e.g. even if theheritabilty of a trait, like intelligence were found to be 100% it wouldn’t mean it couldn't be modified. (Anastasi & Urbina, 1997).

In the discussion to date, we have focused on the heritability (or otherwise) of general intelligence. What about the subcomponents of intelligence? There is, indeed, evidence of a greater genetic link for:

1. Spatial ability2. Reasoning

And less evidence for genetic influence on:

1. Divergent thinking2. Verbal fluency

There is, however, relatively little research along these lines.

Evidence in favour of “nurture”

"Give me a dozen healthy infants & my own specific world to bring them up in, & I'll guarantee to take any one at random & train him to become any type of specialist I might select - doctor, lawyer, artist, merchant, chef & yes, even beggar & thief, regardless of his talents, penchants, tendencies, abilities, vocations, and race of his ancestors."- John B. Watson, 1924

This was a famous quote in the heyday of behaviorism, when the child was considered to be a 'tabula rasa' (blank slate) onto which anything could be sculpted through environmental experience. This would be a 100% environmental view, but virtually no psychologists would accept such an extreme position today.

The Flynn effect: Are we getting smarter?

In the 1980s, a NZ-based political scientist, James Flynn, noticed that IQ was increasing in all countries all the time, at an average rate of about 3 IQ points per decade i.e. the average IQ

across the world has risen over 1 standard deviation (i.e. 15 points) since WWII - predominantly due to environmental effects. As a result, new norms continue to be used to rescale IQ tests to '100'.

Could this be due to diet? Possibly but IQ scores are still rising just as rapidly in well- nourished western countries. Could it be schooling? Interruptions to schooling only have temporary effects on IQ. Importantly, it is those test s that test abstract reasoning ability that show the steepest improvements. One researcher, Ulric Neisser suggests that the Flynn effect is due to the way we are being saturated with sophisticated visual images: ads, posters, videogame and TV graphics etc - rather than written messages. He suggests that children experience a much richer visual environment than in the past and that this assists them with visual puzzles of the kind that dominate IQ tests.

The evidence for the rise in IQ comes from:• Adoption studies• Nutrition studies• Educational intervention studies

Intelligence varies with at least 21 factors

Some of the other circumstances and attributes that have been found to vary to a greater or lesser (but always significant) extent in relation with IQ (Bouchard & Segal, 1985; Liungman, 1975) - note that not all of these relationships support an environmental view.

Intelligence varies with:

Infant malnutrition (-ve) Birth weight Birth order Height Number of siblings (-ve) Number of years in school Social group of parental home Father's profession Father's economic status Degree of parental rigidity (-ve) Parental ambition Mother's education Average TV viewing (-ve) Average book-reading Self-confidence according to attitude scale measurement Age (negative relationship, applies only in adulthood) Degree of authority in parental home (-ve) Criminality (-ve) Alcoholism (-ve) Mental disease (-ve) Emotional adaptation

"No single environmental factor seems to have a large influence on IQ. Variables widely believed to be important are usually weak....Even though many studies fail to find strong environmental effects....most of the factors studied do influence IQ in the direction predicted by the investigator....environmental effects are multifactorial and largely unrelated to each other."- Bouchard & Segal (1985), p.452

So, it would appear that there are many psychological and biological factors each contributing a small a small fraction to the variance in IQ scores.

Intelligence & race

Let's focus on some of the correlates of intelligence examining in particular the interplay between race, environment and intelligence; between SES, environment and intelligence; between education, environment and intelligence; and between occupation, environment and intelligence.

Herrnstein and Murray (1994) in The Bell Curve state that :• Asians and Asian-Americans have a (.32 standard deviation) higher average IQ than whiteAmericans, and that

• white Americans have a (1.58 standard deviation) higher mean IQ than black Americans.

Further, they claim that this difference is not a function of cultural testing bias.

Herrnstein and Murray (1994) acknowledge that the causes of these differences could be environmental, however the differences in IQ appear to be too large to be accounted for by environmental influences alone. They provide much qualification, cautioning, and warnings about how their evidence should be interpreted and used. In particular, they remind the reader that• IQ is not strongly linked to many so-called 'desirable' human qualities; and• The fallacy of drawing conclusions about individual on the basis of group findings.

It would be incorrect to characterize "The Bell Curve" as out-and-out a racist, eugenicist, etc. book. Even detractors acknowledge the importance of its contribution to psychological and social debate. But the book does, in general, support a view that intelligence is largely heritable.

Note that there have also been investigations into racial differences on subcomponents of intelligence. Herrstein and Murray (1994) report that:• East Asian scores are typically the same or slightly lower than White American scores onverbal IQ, but much higher on visuo-spatial IQ• Black Americans tend to score higher than whites on subtests involving arithmetic and immediate memory, whereas whites typically score high than blacks on subtests of spatial-perceptual ability

Differences in IQ scores between races does not necessarily imply genetic causes. Most psychologists accept that there are group mean differences in IQ scores for non-culturally- loaded tests. However, these differences are confounded with the effects of SES, e.g.

1. Children with black fathers, brought up in white family - no evidence of lower IQs2. Adoption studies - e.g. black children brought up by white families only slightly lower IQs than white adopted children (Howe, 1997)

Some theorists suggest that socioeconomic disadvantages are the main causes of ethnic differences in IQ.

Even if the variation within a group reflects genetic differences, the average differences between the groups could be wholly due to environmental factors. Imagine, two pots, with randomly allocated seeds from the same batch. The two plots have equivalent genetic potential. One plot received fertilizer (an environmental condition), the other pot receives no fertilizer. The average height (i.e. intelligence) differences between each pot will be due to environmental differences (fertilizer), however the height differences amongst individual plants within a pot are due to genetic differences (assuming similar conditions throughout the

Nature vs Nurture in Intelligence

pot).

There is debate about whether heritability estimates even matter, since they can't be applied toan individual or be used to help people:

Wahlsten (1997, p. 84) states that:

"It does not matter whether the field of human behavior genetics finally decidesthat the heritability of IQ in the United States is 25%, 40%, 50%, or 70%. Any such estimate will be utterly useless to anyone seeking better ways to improve the intelligence of the nation through health care and education."

Intelligence & socioeconomic status

Herrstein and Murray (1994) argue that low intelligence causes low SES, rather than the otherway around. So, according to these authors, while SES is correlated with IQ, it should be considered a consequence rather than a cause.

However, adoption studies seem to indicate that SES has a strong, causal effect on intelligence, e.g.:

"Well-controlled adoption studies done in France have found that transferring an infant from a family having low socioeconomic status (SES) to a home where parents have high SES improves childhood IQ scores by 12 to 16 pointsor about one standard deviation, which is considered a large effect size in psychological research." Wahlsten (1997, p. 76).

Several recent US studies have demonstrated improvements in children's IQ's by improving the lives of infants in disadvantaged circumstances.These studies employed random assignment of children and families to treatment and control conditions.

These studies selected families with:• low parental IQ• low parental education• minimal financial resources

Experimental group received:• enriched, educational day care outside the home every weekday from 3 months to start of schooling

Control group received:• nutritional supplements and pediatric medical care or crisis intervention but no educational

Nature vs Nurture in Intelligence

day care

Even though the children returned to their home environment every day and spent holidaysand weekends with their families (mostly unemployed, single mothers) in poverty-stricken neighbourhoods, there were large gains in IQ; almost as much as in the French studies previously mentioned.

Furthermore, the mean IQ of the enriched groups appeared to be quite typical of healthy American children. These children continued to show higher IQ scores than controls at age 12(Wahlsten, 1997). Of course, in these American studies, SES and education were being manipulated. There is of course a strong correlation between SES and education in both directions.

Intelligence & education

A number of studies have shown that schooling and intelligence influence each other. Higher intelligence tends to lead to prolonged schooling and longer schooling leads to higher IQ.

Intelligence at age 5 predicts better than any other variable a child's future educational progress and attainment (Kline, 1991).

Wahlsten (1997):• delays in schooling cause IQ to 'drop' 5 points per year• temporary drop in IQ during school vacations

Winship & Korenman (1997):• 2.7 IQ point advantage for each year of schooling• thus to predict later IQ, two estimates are useful: early IQ estimates and number of years of schooling

A study by Cahan and Cohen, found that older children in a grade tended to score slightly higher than their younger classmates but importantly they found that children who are in a higher grade but are virtually the same age as children in the grade lower have higher IQ scores. It is postulated this is due to the extra year of schooling.

However a number of authorities believe that enriched or increased schooling has little effect on intelligence and have refute the suggestion that intelligence can be modified.

"Compensatory education has been tried and it apparently has failed."- Jensen, 1969

"the story of attempts to raise intelligence is one of high hopes, flamboyant claims, and disappointing results."- Herrstein & Murray (1994), p.389

One justifiable criticism levelled at educational enrichment studies conclusions about increased IQ is that what is being modified is performance on a test rather than an actualmodification in intelligence. Children in enrichment programmes often receive extensiveinstruction and practice in test-taking. “What has been temporarily modified in the early stages of early intervention programmes is performance on a test, not the child’s general intelligence” (Herman Spitz, 1999, p. 289).

This would account for the well-known fade-out effect, whereby initial, often very high gains in IQ scores, in experimental “enriched schooling” groups, return to the level of the control group a few years after the “experiment”.

In the US a large nationwide programme, the Head Start programme, aims to enrich the schooling of disadvantaged children. On the whole, the results have been mixed. Head Start

and programmes like it have been criticized for not living up to expectations in changing IQ.The main defense is that the primary aim is not to improve IQ, but to accelerate academic development - IQ change is a bonus, academic development is more important.

Head Start type programmes have also been criticized for not effecting last changes. This isnot surprising if children return to poor, unsupportive, deprived environments. And, in fact,such a finding supports the idea that IQ is malleable - in both directions.

New and better ways of educating, improving, and maximizing individual potentials in intelligence are likely to be developed. As this happens, more and more of the environmentally-influenced variation in IQ is likely to come under control and estimates of the 'environment' proportion could increase.

Intelligence & occupation

"In more than 10,000 studies the average correlation of IQ with occupational success was 0.3...this correlation is certainly a low estimate of its true size...no other variable, either of ability or personality, can approach this figure."- Kline (1991), p. 139

Herrstein and Murray estimate the relationship between IQ and occupation to be between .2 and .6 (i.e. that IQ explains between 4% and 36% of the variations in occupation). These correlations are slightly higher for skilled, professional jobs, and slightly lower for jobs that require less skill. Whilst this might be useful in describing groups, it means there is questionable value in administering an IQ test to an individual in an attempt to help determinetheir occupational options. It may be a useful approach, however, to help select the best 100 employees from a 1000 applicants (Howe,1997, p.97).

Comments on the scope & quality of intelligence research

All this research uses psychometric, quantitative tests of intelligence, which we know from previous lectures corresponds somewhat (but not entirely) with our conceptions of what intelligence is.

The research is very focused on North American populations.

Multiple intelligences or subcomponents of intelligence are barely considered in much of this research. Neither are alternative measures of intelligence, such as speed of processing, evoked potentials, or practical intelligence, etc.

Future research on brain-behaviour connections will probably help to more accurately isolate the functions of 'intelligence' (Weinberg, 1989).

In addition, as we come to understand and develop more effective environmental interventions to maximise individuals' IQs, this will possibly expand the relative important ofthe 'nurture' component.

Nevertheless, there remains the spectre of eugenics - those who would argue for selective breeding on the basis of intellectual ability. This issue is likely to rear its head again in the future and with new genetic technologies could appear in a more dynamic form.

The role of “interaction"

An underresearched area, while the nature vs. nurture debate has raged, is the contribution of interactions between genetics and environment on IQ variance.In the overfocus on nature vs. nurture issues, the attempts to estimate the relative contribution rests on the somewhat naive notion that there is a constant, true value. In reality, "gene expression is environment dependent" and it impossible to obtain pure estimates of genetic vs. environmental contribution - one could not exist without the other.The environment a child experiences is partly a consequence of the child’s genes as well as external factors. To some extent a person seeks out and creates his or her environment. If she is of a mechanical bent she practices mechanical skills; if a bookworm, she seeks out books. Thus genes may create an appetite rather than an aptitude. Remember that the high heritabilityof short-sightedness is accounted for not just by the heritability of a gene for short sightednessbut by the heritability of literate habits.Thus, a future area for research which blends those in the nature camps with those in the nurture camps would be examine which environmental components allow people to optimallyrealise their genetic potentials for a variety of areas of cognitive performance (e.g. see Feldman, 1986).

What have we learnt about intelligence?

So, what can we say about nature vs. nurture as causal determinants of intelligence? A conservative, seemly safe position is that:"In the field of intelligence, there are three facts about the transmission of intelligence that virtually everyone seems to accept:

1. Both heredity and environment contribute to intelligence.2. Heredity and environment interact in various ways.3. Extremely poor as well as highly enriched environments can interfere with the realization of a person's intelligence, regardless of the person's heredity” (Sternberg & Grigorenko, 1997,p.xi).

4. Although most would accept a causal role of genetics, the exact genetic link and how itoperates is very far from being understood - another point that most psychologists would agree on. It is certainly not a single gene, but a complex combination of smaller genetic markers.5. But likewise, it is difficult to pin-down single, identifiable elements of the environmentwhich directly influence IQ scores. Several environmental factors influence intelligence.

So what have we learned about intelligence: that it’s difficult to define but that there is SOMETHING we call intelligence that appears to relate to ability to reason abstractly, to learn and to adapt. That we can measure some part of it, although poorly; that it’spartially caused by genetics, partially be environment; that the real causes are the complex, not well understood interplay between genetics and environment; that it is somewhat though not greatly modifiable; that sometimes what we learn from tests is used inappropriately but that IQ tests can be useful in helping children attain their potential.

Final quotes

"Measures of intelligence have reliable statistical relationships with important social phenomena, but they are a limited tool for deciding what to make of any given individual. Repeat it we must, for one of the problems of writing about intelligence is how to remind readers often enough how little an IQ score tells you about whether the human being next to you is someone whom you will admire or cherish." Herrnstein and Murray (1994, p. 21)

"Mother Nature has plainly not entrusted the determination of our intellectual capacities to the blind fate of a gene or genes; she gave us parents, learning, language, culture and education to program ourselves with."(Ridley, 1999, p. 77)

References

Anastasi, A., & Urbina, S. (1997). Psychological Testing (7th ed.). Upper Saddle River, NJ: Prentice-Hall.

Bouchard, T. J., & Segal, N. L. (1985). Environment and IQ. In B.B. Wolman (Ed.). Handbook of Intelligence: Theories, Measurements, and Applications (pp. 391-464). New York: John Wiley.

Daniels, M., Devlin, B., & Roeder, K. (1997). Of genes and IQ. In B. Devlin, S. E. Fienberg.,& K. Roeder (pp. 45-70). Intelligence, Genes, and Success: Scientists respond to The Bell Curve. New York: Springer.

Devlin, B., Fienberg, S. E., Resnick, D. P., & Roeder, K. (Eds.) (1997). Intelligence, Genes, and Success: Scientists respond to The Bell Curve. New York: Springer.

Eysenck, H. (1971). Race, Intelligence and Education. London: Maurice Temple Smith.

Feldman, D. H. (1985). Nature's Gambit: Child Prodigies and the Development of Human Potential. New York: Basic Books.

Gottfredson, L. S. (1997). Mainstream science on intelligence: An editorial with 52 signatories, history, and bibliography. Intelligence, 24, 13-23.

Herrnstein, R. J., & Murray, C. (1994). The bell curve. New York: The Free Press.

Howe, M. J. A. (1997). IQ in Question: The truth about intelligence. London: Sage.

Jensen, A. R. (1969). How much can we boost IQ and scholastic achievement? Harvard Educational Review, 39, 1-123.

Kline, P. (1991). Intelligence: The Psychometric View. London: Routledge.

Liungman, C.G. (1975). What is IQ? Intelligence, Heredity and Environment. London: Gordon Cremonesi.

Manolakes, L. A. (1997). Cognitive Ability, Environmental Factors, and Crime: Predicting Frequent Criminal Activity. In B. Devlin, S.E. Fienberg., & K. Roeder (pp. 235-255).Intelligence, Genes, and Success: Scientists respond to The Bell Curve. New York: Springer.

Ridley, M. (1999). Genome: The autobiography of a species in 23 chapters. London: Fourth Estate Ltd.

Sternberg, R. J., & Grigorenko, E. (Eds.) (1997). Intelligence, heredity, and environment. Cambridge, UK: Cambridge University Press.

Wahlsten, D. (1997). The malleability of intelligence is not constrained by heritability. In B. Devlin, S.E. Fienberg., & K. Roeder (pp. 71-87). Intelligence, Genes, and Success: Scientists respond to The Bell Curve. New York: Springer.

Weinberg, R.A. (1989). Intelligence and IQ: Landmark issues and great debates. American Psychologist, 44, 98-104.

Winship, C., & Korenman, S. (1997). Does staying in school make you smarter? The effect ofeducation on IQ in The Bell Curve. In B. Devlin, S.E. Fienberg., & K. Roeder (pp. 215-234). Intelligence, Genes, and Success: Scientists respond to The Bell Curve. New York: Springer.