Outline
• David Wechsler – some history• Wechsler’s Scales• IQ scores• Index scores• Verbal subtests• Performance subtests• WAIS Psychometrics
David Wechsler (1896 – 1981)
• Studied at Columbia University (M.A., 1917; Ph.D., 1925)
• Went to France with US Army in 1919, then to London
• Studied with Pearson & Spearman
• Also with Anna Freud in Vienna
David Wechsler
• Worked at NY’s Bellevue Hospital.• Unhappy with the Stanford-Binet
– Content appropriate only for children– Rapport problems if used with adults– Produces only a single score– Norms not appropriate for adults– Binet’s emphasis on speed hurt older adults’ scores
Wechsler Scales
• 1939: the Wechsler-Bellevue, later called the WAIS.• 1945: the Wechsler Memory Scale• 1949: the children’s version, the WISC• 1955: Wechsler Adult Intelligence Scale• 1967: the WPPSI for children ages 2½ -7• 1981: WAIS-R (revised form of 1955 test)• 1997: WAIS-III
Wechsler Scales
“Intelligence is the aggregate or global capacity of the individual to act purposefully, to think rationally and to deal effectively with his environment.”David Wechsler (1939)
• global: one score ultimately describes a person’s intellectual ability• aggregate: that one score is composed of a number of sub-scores
Wechsler’s original test
• Wechsler believed that intellectual ability involves two major types of skills: verbal and performance abilities.
• Each of these broad types includes a variety of specific skills that are assessed by the various subtests of the WAIS.
• However, all these subtests measure g as well as specific skills
Full Scale IQ
Verbal IQ Performance IQ
VCI WMI POI PSI
VocabularySimilaritiesInformationComprehension
Digit SpanArithmeticLetter-Number Sequencing
Block DesignMatrix reasoningPicture completionPicture arrangement
Digit-Symbol CodingSymbol Search
Wechsler test produced 3 IQ scores
• Full-scale IQ: • reflects both verbal and performance IQs
• most reliable and valid score extracted from WAIS
• why do you think this is the most reliable?
Wechsler test produced 3 IQ scores
• Verbal IQ: • Responses require person being tested to use language – to understand instructions or to make a response
Wechsler test produced 3 IQ scores
• Performance IQ: • Performance subtests involve doing something, not just answering questions
Structure of the WAIS
• WAIS-III has four index scores: – verbal comprehension– working memory– perceptual organization– processing speed.
• Index scores added recently because, with new subtests, factor analysis suggests these four factors
Index scores
• Verbal comprehension • assesses general verbal skills, such as verbal fluency, ability to understand and use verbal reasoning, and verbal knowledge
• based on both formal and informal educational opportunities,
Index scores
• Working memory• “The blackboard of the
mind” (Goldman-Rakic, 1992)
• Encode information into STM, store it there, retrieve it when needed
• Manipulate information (e.g., addition)
• Thinking, learning, planning
Index scores
• Perceptual organization • Use visual, spatial, and visually-guided motor skills
• Organize thoughts• Assesses comfort with
new, unfamiliar situations
Index score
• Processing speed• The speed at which
cognitive processes can be carried out
• focus, scanning speed, sequentially ordering visual information
• sensitive to motivation, difficulty working under time pressure.
• biological• cultural factors have little
impact
WAIS Verbal Tests
• Vocabulary• Similarities• Arithmetic• Digit Span• Information• Comprehension• Letter-Number Sequencing
Vocabulary
• Subject is given one word at a time, asked to define it
• Sensitive to word knowledge, linguistic development, acquired knowledge, verbal expression ability, crystallized intelligence
• The best single measure of g
• Correlation of vocabulary score with g is .83
Vocabulary
• Very stable• Resistant to effects of
poor concentration in schizophrenia
• Not affected by mild concentration trouble
• Of all WAIS subtests, the one most resistant to brain damage
• Thus, allows a good estimate of pre-morbid functioning
Similarities
• Task is to say how two (superficially) dissimilar items might be similar
• Evaluating details – which details are “diagnostic”?
• Earlier items in series are known through experience (e.g., “In what way are a cake and a pudding alike?”)
• Later items require abstract thinking (e.g., “How are affection and approval alike?”
Similarities
• Logical, abstract thinking
• Concept formation • Crystallized and fluid
intelligence
• With Information subtest, the second best for measuring g
• Correlation with g =.79
Similarities
• Of VCI (Verbal Comprehension Index) subtests, the one least affected by formal education or learning
• Score on this subtest is impacted by psychopathology, and by brain damage – esp. left hemisphere lesions
Arithmetic
• Assesses working memory, numerical reasoning, computation skill, concentration, retrieval from LTM
• Influenced by emotional state
• Correlation with g is r = .75
Digit Span
• Repeat a series of up to 7 digits in correct order
• Digits presented 1 per second
• Tested both Forward (DSF) and Backward (DSB)
• Attention, auditory memory and sequencing, short term memory, mental alertness, sequential processing, cognitive flexibility
Digit Span
• Average 6.4 digits forward, 4.7 backwards
• DSF – DSB ≥ 5 suggests brain damage
• Correlation with g: r=.57 (the worst)
Information
• Acquired knowledge, crystallized intelligence, fund of information, range of general factual knowledge, long term memory
• Affected by formal education opportunities
• Correlation with g: r = .79 (2nd best)
• Failure on easy items followed by success on harder items suggests retrieval difficulties
• Resistant to psychopathology and brain damage – good estimate of pre-morbid functioning
Comprehension
• 3 different kinds of questions:– Appropriate responses
to hypothetical situations
– Logical explanations for everyday actions
– Proverb interpretations
• Assesses social and moral reasoning, judgment, verbal concepts, knowledge of ordinary standards of behavior, practical information
Comprehension
• Rewards conventional responses, not creative ones
• R Hem patients may score high (their L Hem intact so they know answers) but still behave inappropriately
• g: correlation r = .77
Letter-number sequencing
• Optional – not needed to compute IQ
• Task is to re-order intermixed, randomly-sequenced numbers and letters
• Taps STM, sequential reasoning ability, planning
• g: correlation r = .65• Impaired by anxiety,
weak attention focusing ability
• Dropping a letter: attention problem
• Mixing up letters: sequencing problem
WAIS Performance Tests
• Picture completion• Digit symbol-coding• Block design• Matrix reasoning• Picture arrangement• Symbol search (optional)• Object assembly (optional)
Picture Completion
• Task: say what detail is missing from a picture.
• Timed response• Pointing response is
allowed• Raises issue of pointing
precision (trained examiner required)
• Alertness, attention to detail
• LTM (Visual)• Crystallized intelligence• R Hem skill• g: correlation r = .64
Digit Symbol Coding
• Visual STM• Psychomotor speed• Visual-motor
coordination• Visual sequencing• Accuracy & speed
• g: correlation r = .59• Very sensitive to any
kind of brain damage
Block Design
• Assesses visual-motor coordination, visual analysis & synthesis, spatial visualization
• Visual input, motor output
• Fluid intelligence• Trial & error learning
• g: correlation = .72• Affected by R Hem
damage• Bizarre solutions may
indicate dementia
Matrix Reasoning
• 4 types of stimuli:– pattern completion– classification– analogy– serial reasoning
• Subject given a series of matrices and must say what goes in the empty cell
Ō ō Ǒ ?
Matrix reasoning
• Measures abstract thinking, nonverbal reasoning, analogy skill
• Fluid intelligence• Visual organization
• g: correlation r = .72
Picture Arrangement
• Task is to put a series of (randomly-ordered) pictures into narrative order (so they tell a coherent story)
• As if you found a comic strip jumbled up and had to order the frames sensibly
• Non-verbal reasoning• Possibly social skill• Fluid & crystallized
intelligence• Planning• Time concepts
Picture Arrangement
• Failure may be due to visual problems (compare with Picture Completion)
• g: correlation r = .66
Symbol Search
• Optional – not needed to compute IQ
• Subject shown two target abstract symbols and asked whether either target appears in a set of ‘probe’ symbols
• 120 seconds allowed• How many can subject
do in that time?
Symbol Search
• Visual-motor coordination and speed, planning, STM, perceptual speed
• Large practice effects in young adults
• g: correlation r = .70
Object Assembly
• Subject given pieces of a puzzle
• Task is to assemble pieces into a whole
• Taps knowledge of part-whole relationships, visual-motor coordination, anticipation of relationships among parts
• Fluid intelligence
Object Assembly
• Sensitive to cerebral damage, especially in R Hem
• Sensitive to disorder called neglect
• g: correlation r = .62
Scales and Norms for the WAIS• Determine raw score for each subtest.• Convert raw scores to standard scores, called
scaled scores (M=10, SD=3)• Convery to standard scores using tables for age
(13 age groups).• Subtest scaled scores are added, then converted
to WAIS-III composite scores.• Three composite scores: Verbal, Performance,
Full Scale, each with M=100, SD=15
Standardization of the WAIS
• Standardized on a stratified sample of 2,450 adults representative of the US population aged 16-89.
• There were 200 cases per age group, except for the smaller numbers in the two oldest groups.
• Still difficult to know the effects of self-selection since participants had to be invited and accept to be included.
Reliability of the WAIS
• Internal consistency and test-retest reliabilities .95 or higher for full scale and verbal scores.
• About .90 for performance and these index scores: perceptual organization, working memory, and processing speed.
Reliability of the WAIS
• Internal consistency reliability for the subtests range from upper .70s to low .90s. Test-retest is about .83.
• Generally, performance reliabilities are lower than verbal reliabilities on the subtests.
• Why might that be?
Validity of the WAIS
• We have a great deal of information on criterion-related and construct validity.
• Factors analyses support use of 4 index scores.
• Most widely used ability test today
Johnson et al. (2004)
• Measured correlation between WAIS scores and two other test batteries:– Comprehensive Ability Battery (CAB)– Hawaii Battery + Ravens
• These batteries varied in their subtests, but correlations were essentially perfect
Comprehensive Abilities Battery1. Numerical Ability Computations including fractions, decimal divisions,
square roots, etc.2. Spatial Ability Interpretation of two-dimensional figural rotation or
reversal.3. Memory Span Recall of digits presented aurally.4. Flexibility of Closure Identification of embedded figures.5. Mechanical Ability Identification of mechanical principles and tools.6. Speed of Closure Completion of gestalt.7. Perceptual Speed Evaluation of symbol pairs.8. Word Fluency Production of anagrams.9. Inductive Reasoning Identification of pattern in sequences of letter sets.10. Associative Memory Rote memorization of meaningless pairings.11. Meaningful Memory Rote memorization of meaningful pairings.12. Verbal—Vocabulary Multiple choice among possible synonyms.13. Verbal—Proverbs Interpretation of proverbs.14. Spelling Multiple-choice identification of misspellings.
Hawaii Battery + Ravens15. Card Rotations Matching of rotated alternatives to probe.16. Mental Rotation Identification of rotated versions of 2-D pre-presentation of 3-D objects.17. Paper Form Board Outline of cutting instructions to form the target figure.18. Hidden Patterns Identification of probe figures in more complex patterns.19. Cubes Identification of matched figures after rotation.20. Paper Folding Identification of unfolded version of a folded probe.21. Raven Identification of analogous figure to follow a sequence of figures.22. Vocabulary Multiple choice among possible meanings.23. Subtractn/Multn Completion of two-digit subtractions and two-digit by one-digit
multiplications.24. Word Beg/Endings Generation of words beginning and ending with specified letters.25. Pedigrees Identification of familial relationships within a family tree.26. Things Categories Generation of things that share assigned characteristics.27. Different Uses Generation of novel uses for specified objects.28. Immed Vis Mem Recall of illustrations of common objects immediately following
presentation.29. Delay Visl Mem Recall of illustrations of same common objects after delay.30. Lines and Dots Trace a path through a grid of dots.31. Identical Pictures Identification of alternative identical to probe.
Johnson et al. (2004)
• Correlations:• WAIS – Hawaii Battery + Ravens 1.00• WAIS – Comprehensive Ability Battery 0.99• Hawaii – CAB
0.99
• These results constitute strong evidence for g and show that the one-factor result does not depend upon particular tasks
WISC-III
• Most popular test for assessing intellectual ability of children ages 6 years, 0 months to 16 years, 11 months.
• Similar to structure of the WAIS, with easier items
• Both tests yield verbal, performance, and full scale IQ and 4 index scores
• Most of the subtests are the same
Psychometric Properties of the WISC-III
• Standardization program involved 2,200 cases selected to represent the US population of children aged 6-16.
• Composite scores generally have internal consistency reliabilities in the mid-.90s and test-retest reliabilities around .90.
• Subtest reliabilities are generally in the mid-.80s.• Object Assembly and Mazes are problematic, with
reliabilities in the .60s.