Variables in Educational Variables in Educational ResearchResearch

Most used term in research.Most used term in research. A variable is a label or name that represents A variable is a label or name that represents

a concept or characteristic.a concept or characteristic. Concept—noun that stands for a class of Concept—noun that stands for a class of

objects, e.g., tree, house, teacher, desk, and objects, e.g., tree, house, teacher, desk, and school.school.

Characteristic—a trait we use to describe Characteristic—a trait we use to describe things, e.g., tall, male, creative, or average.things, e.g., tall, male, creative, or average.

VariablesVariables

A variable--Any entity that may take one of A variable--Any entity that may take one of two or more mutually exclusive valuestwo or more mutually exclusive values

EXAMPLES:EXAMPLES: Sex--any one of two mutually exclusive Sex--any one of two mutually exclusive

values: female & malevalues: female & male Day of the week--any one of seven Day of the week--any one of seven

mutually exclusive valuesmutually exclusive values Age--a large number of mutually exclusive Age--a large number of mutually exclusive

values.values.

Discrete and Continuous Discrete and Continuous VariablesVariables

A discrete variable--categorical and differ A discrete variable--categorical and differ qualitatively, e.g. sex, day of the week.qualitatively, e.g. sex, day of the week.

A continuous variable--takes on an infinite A continuous variable--takes on an infinite number of values that differ from each other number of values that differ from each other quantitatively, e.g. age. quantitatively, e.g. age.

Variable definition determines intent of Variable definition determines intent of researchresearch

Two types of variable definitionTwo types of variable definition

Constitutive definition—uses words or concepts to Constitutive definition—uses words or concepts to describe variable, e.g., describe variable, e.g., attitudeattitude—“a predisposition —“a predisposition to respond favorably or unfavorably toward a to respond favorably or unfavorably toward a person, object or event.”person, object or event.”

Operational definition—indicates the operations Operational definition—indicates the operations that are performed to measure the variable--uses that are performed to measure the variable--uses techniques that measure or produce the variable.techniques that measure or produce the variable.• Researchers use different ways of measuring or Researchers use different ways of measuring or

manipulating the same variable. manipulating the same variable.

Variables as a set of valuesVariables as a set of values

Institution

Hospital School

Public School Private School

Nonsectarian School Parochial School

3 Basic Ways of Examining 3 Basic Ways of Examining VariablesVariables

To describe how the values associated with To describe how the values associated with one or more variables are distributed among one or more variables are distributed among one or more groups of people--one or more groups of people--DESCRIPTIVE RESEARCHDESCRIPTIVE RESEARCH

To determine the nature of the relationship To determine the nature of the relationship between two or more variables among a between two or more variables among a single group of people--single group of people--CORRELATIONAL CORRELATIONAL STUDIESSTUDIES

3 Basic Ways of Examining 3 Basic Ways of Examining Variables (cont.)Variables (cont.)

To examine the extent to which two or To examine the extent to which two or more groups of people exhibit different more groups of people exhibit different values with respect to a single variable--values with respect to a single variable--GROUP COMPARISON STUDIESGROUP COMPARISON STUDIES

Populations and SamplesPopulations and Samples

PopulationsPopulations are groups consisting all the are groups consisting all the people that researchers wish to apply their people that researchers wish to apply their findings.findings.

SamplesSamples are group of people representing are group of people representing subsets of populations.subsets of populations.

Independent and Dependent Independent and Dependent VariablesVariables

What is Correlational Research?What is Correlational Research?

Correlational ResearchCorrelational Research Correlational research attempts to determine Correlational research attempts to determine

whether, and to what degree, a relationship whether, and to what degree, a relationship exists between two or more quantifiable exists between two or more quantifiable variables.variables.

The purpose of correlational study may be The purpose of correlational study may be to establish relationship (or lack of it) or to to establish relationship (or lack of it) or to use relationships in making predictions.use relationships in making predictions.

Examples of Correlational Examples of Correlational StudiesStudies

1. The relationship between intelligence and 1. The relationship between intelligence and self-esteem.self-esteem.

2. The relationship between anxiety and 2. The relationship between anxiety and achievement.achievement.

3. Use of an aptitude test to predict success 3. Use of an aptitude test to predict success in an algebra course.in an algebra course.– (Show how you will correlate the scores in (Show how you will correlate the scores in

each of the studies).each of the studies).

Group Comparison StudiesGroup Comparison Studies Examines how the values associated with a Examines how the values associated with a

single variable may be distributed single variable may be distributed differently among two or more groups of differently among two or more groups of people.people.– EXAMPLE: How do the self-concepts of EXAMPLE: How do the self-concepts of

special education children who have been special education children who have been mainstreamed differ from the self-concepts mainstreamed differ from the self-concepts of special education children in self-of special education children in self-contained classrooms? (Which is the variable contained classrooms? (Which is the variable and which are the two groups?)and which are the two groups?)

GROUP WORKGROUP WORK Give an example of group comparison Give an example of group comparison

studies. Identify the variable that can take studies. Identify the variable that can take on one of two values. on one of two values.

Populations, Samples, and Populations, Samples, and SubjectsSubjects

Populations are groups consisting of all Populations are groups consisting of all people to whom researchers wish to apply people to whom researchers wish to apply their findings.their findings.

Samples are groups of people (representing Samples are groups of people (representing subsets of populations) from whom data are subsets of populations) from whom data are collected.collected.

Subjects are individuals who participate in a Subjects are individuals who participate in a research study or people from whom data research study or people from whom data are collected.are collected.

The Target Population and the The Target Population and the Accessible PopulationAccessible Population

Target population--the population the Target population--the population the researcher would like the results to be researcher would like the results to be generalized.generalized.

Accessible population--the population Accessible population--the population available from which the researcher can available from which the researcher can select.select.

GROUP WORKGROUP WORK Choose a research question and identify (a) Choose a research question and identify (a)

the target population and (b) accessible the target population and (b) accessible population.population.

List examples of research List examples of research populations and samplespopulations and samples

In the United StatesIn the United States Oregon Oregon Washington CountyWashington County In Forest GroveIn Forest Grove In Pacific UniversityIn Pacific University EDUC 601 class.EDUC 601 class.

Purpose of SamplingPurpose of Sampling The purpose of sampling is to obtain a The purpose of sampling is to obtain a

group of subjects who will be representative group of subjects who will be representative of the larger population or will provide of the larger population or will provide specific information needed.specific information needed.

SamplingSampling

1. Probability Sampling--selecting a sample 1. Probability Sampling--selecting a sample that will adequately represent the true that will adequately represent the true population.population.– (a) Random Sampling--each member of the (a) Random Sampling--each member of the

population has the same probability of being population has the same probability of being selectedselected..

Sampling (cont.)Sampling (cont.)– (b) Systematic Sampling--every Nth member (b) Systematic Sampling--every Nth member

of the population is selectedof the population is selected– (c) Stratified Sampling--subjects are selected (c) Stratified Sampling--subjects are selected

from groups of the populationfrom groups of the population– (c) Cluster Sampling--Naturally occuring (c) Cluster Sampling--Naturally occuring

groups are selectedgroups are selected

Example of a Study using Example of a Study using Probability SamplingProbability Sampling

What is the attitude of teachers in the North What is the attitude of teachers in the North Country toward unions?Country toward unions?

1. The population is 5,000 teachers.1. The population is 5,000 teachers. 2. The desired sample size is 10% of the 2. The desired sample size is 10% of the

5,000 teachers, or 500 teachers.5,000 teachers, or 500 teachers. 3. We have a directory which lists all 3. We have a directory which lists all

teachers in the system.teachers in the system. RANDOM SAMPLING--RANDOM SAMPLING--

Steps in SYSTEMATIC Steps in SYSTEMATIC SAMPLING:SAMPLING:

1. The population is all 5,000 teachers.1. The population is all 5,000 teachers. 2. The desired sample is 500.2. The desired sample is 500. 3. You have a directory which lists all the teachers 3. You have a directory which lists all the teachers

in alphabetical order.in alphabetical order. 4. Nth is equal to the size of the population, 5,000 4. Nth is equal to the size of the population, 5,000

divided by the size of the sample. Thus Nth = divided by the size of the sample. Thus Nth = (5,000 divided by 500) = 10.(5,000 divided by 500) = 10.

5. Select a random name at the top of the list of 5. Select a random name at the top of the list of teachers.teachers.

Steps in SYSTEMATIC Steps in SYSTEMATIC SAMPLING: (cont.)SAMPLING: (cont.)

6. From that point, every following 10th 6. From that point, every following 10th name is in the sample.name is in the sample.

Steps in STRATIFIED Steps in STRATIFIED SAMPLINGSAMPLING

1. The population is all 5,000 teachers.1. The population is all 5,000 teachers. 2. Desired sample size is 10% of the 5,000 2. Desired sample size is 10% of the 5,000

teachers, or 500 teachers.teachers, or 500 teachers. 3. The variable of interest is teaching level 3. The variable of interest is teaching level

and there are three subgroups--elementary, and there are three subgroups--elementary, junior high, and senior high.junior high, and senior high.

4. Randomly select 10% of each subgroup 4. Randomly select 10% of each subgroup to represent each teaching group to represent each teaching group proportionally.proportionally.

Steps in CLUSTER SAMPLINGSteps in CLUSTER SAMPLING 1. The population is all 5,000 teacher.1. The population is all 5,000 teacher. 2. The desired sample size is 500.2. The desired sample size is 500. 3. A logical cluster is a school.3. A logical cluster is a school. 4. You have a list of all the schools in the 4. You have a list of all the schools in the

North Country; they are 100 schools.North Country; they are 100 schools. 5. There is an average of 50 teachers per 5. There is an average of 50 teachers per

school.school.

Steps in CLUSTER SAMPLING Steps in CLUSTER SAMPLING (cont.)(cont.)

6. The number of clusters (schools) needed 6. The number of clusters (schools) needed equals the desired sample size, 500, divided by equals the desired sample size, 500, divided by the average size of a cluster, 50. Thus, the the average size of a cluster, 50. Thus, the number of schools needed is 500 divided by 50 number of schools needed is 500 divided by 50 = 10.= 10.

7. Therefore, 10 of the schools are randomly 7. Therefore, 10 of the schools are randomly selected.selected.

8. All the teachers in each of the 10 schools are 8. All the teachers in each of the 10 schools are in the sample (10 schools, 50 teachers per in the sample (10 schools, 50 teachers per school, equals the desired sample).school, equals the desired sample).

Sampling (cont.)Sampling (cont.) 2. Non-probability Sampling--probability of 2. Non-probability Sampling--probability of

selection unknown.selection unknown.– (a) Convenience Sampling--a group of (a) Convenience Sampling--a group of

subjects selected because of availabilitysubjects selected because of availability– (b) Purposive Sampling--selection of (b) Purposive Sampling--selection of

particularly informative or useful subjects.particularly informative or useful subjects.– (c) Quota Sampling--nonrandom sampling (c) Quota Sampling--nonrandom sampling

representative of a target population.representative of a target population.

Sampling (cont.)Sampling (cont.) 3. Volunteer Samples--asking for 3. Volunteer Samples--asking for

volunteers.volunteers.

Validity and Reliability of Validity and Reliability of Educational MeasuresEducational Measures

Validity—Validity—the degree to which a test measures what the degree to which a test measures what it is supposed to measureit is supposed to measure..

Was the research process a valid one for answering Was the research process a valid one for answering the research question?the research question?

A test is not valid per se; it is valid for a particular A test is not valid per se; it is valid for a particular purpose and for a particular group.purpose and for a particular group.

Content validity—the degree to which a test Content validity—the degree to which a test measures an intended content area.measures an intended content area.

Construct validity—the degree to which a test Construct validity—the degree to which a test measures an intended hypothetical construct, e.g. measures an intended hypothetical construct, e.g. intelligence.intelligence.

Validity and Reliability of Validity and Reliability of Educational MeasuresEducational Measures

Validity—Validity—the degree to which a test measures what the degree to which a test measures what it is supposed to measureit is supposed to measure..

Was the research process a valid one for answering Was the research process a valid one for answering the research question?the research question?

A test is not valid per se; it is valid for a particular A test is not valid per se; it is valid for a particular purpose and for a particular group.purpose and for a particular group.

Content validity—the degree to which a test Content validity—the degree to which a test measures an intended content area.measures an intended content area.

Construct validity—the degree to which a test Construct validity—the degree to which a test measures an intended hypothetical construct, e.g. measures an intended hypothetical construct, e.g. intelligence.intelligence.

Internal and External ValidityInternal and External Validity

Internal validity—refers to whether the research Internal validity—refers to whether the research process yields a result that is valid in the research process yields a result that is valid in the research context.context.– Is the answer to the research question valid for the Is the answer to the research question valid for the

people on whom the research was done, in the place the people on whom the research was done, in the place the research was done?research was done?

External validity—refers to whether the answer External validity—refers to whether the answer to the research question is valid in a larger to the research question is valid in a larger context—for other people at other times, in context—for other people at other times, in other places.other places.

Validity and Reliability of Validity and Reliability of Educational MeasuresEducational Measures

Validity—Validity—the degree to which a test measures what the degree to which a test measures what it is supposed to measureit is supposed to measure..

Was the research process a valid one for answering Was the research process a valid one for answering the research question?the research question?

A test is not valid per se; it is valid for a particular A test is not valid per se; it is valid for a particular purpose and for a particular group.purpose and for a particular group.

Content validity—the degree to which a test Content validity—the degree to which a test measures an intended content area.measures an intended content area.

Construct validity—the degree to which a test Construct validity—the degree to which a test measures an intended hypothetical construct, e.g. measures an intended hypothetical construct, e.g. intelligence.intelligence.

Internal and External ValidityInternal and External Validity

Internal validity—refers to whether the research Internal validity—refers to whether the research process yields a result that is valid in the research process yields a result that is valid in the research context.context.– Is the answer to the research question valid for the Is the answer to the research question valid for the

people on whom the research was done, in the place the people on whom the research was done, in the place the research was done?research was done?

External validity—refers to whether the answer External validity—refers to whether the answer to the research question is valid in a larger to the research question is valid in a larger context—for other people at other times, in context—for other people at other times, in other places.other places.

ReliabilityReliability

Reliability—dependability, or trustworthiness.Reliability—dependability, or trustworthiness. The degree to which a test The degree to which a test consistentlyconsistently measures measures

whatever it measures.whatever it measures. Expressed numerically as a coefficientExpressed numerically as a coefficient Perfect reliability = 1.00Perfect reliability = 1.00 Very good reliability = greater than .90Very good reliability = greater than .90 Acceptable reliability = between .80 and .90Acceptable reliability = between .80 and .90 Inadequate reliability = below .60Inadequate reliability = below .60

Validity and Reliability of Validity and Reliability of Educational MeasuresEducational Measures

Validity—Validity—the degree to which a test measures what the degree to which a test measures what it is supposed to measureit is supposed to measure..

Was the research process a valid one for answering Was the research process a valid one for answering the research question?the research question?

A test is not valid per se; it is valid for a particular A test is not valid per se; it is valid for a particular purpose and for a particular group.purpose and for a particular group.

Content validity—the degree to which a test Content validity—the degree to which a test measures an intended content area.measures an intended content area.

Construct validity—the degree to which a test Construct validity—the degree to which a test measures an intended hypothetical construct, e.g. measures an intended hypothetical construct, e.g. intelligence.intelligence.

Internal and External ValidityInternal and External Validity

Internal validity—refers to whether the research Internal validity—refers to whether the research process yields a result that is valid in the research process yields a result that is valid in the research context.context.– Is the answer to the research question valid for the Is the answer to the research question valid for the

people on whom the research was done, in the place the people on whom the research was done, in the place the research was done?research was done?

External validity—refers to whether the answer External validity—refers to whether the answer to the research question is valid in a larger to the research question is valid in a larger context—for other people at other times, in context—for other people at other times, in other places.other places.

ReliabilityReliability

Reliability—dependability, or trustworthiness.Reliability—dependability, or trustworthiness. The degree to which a test The degree to which a test consistentlyconsistently measures measures

whatever it measures.whatever it measures. Expressed numerically as a coefficientExpressed numerically as a coefficient Perfect reliability = 1.00Perfect reliability = 1.00 Very good reliability = greater than .90Very good reliability = greater than .90 Acceptable reliability = between .80 and .90Acceptable reliability = between .80 and .90 Inadequate reliability = below .60Inadequate reliability = below .60

Validity vs. ReliabilityValidity vs. Reliability

A valid test is always reliable but a reliable A valid test is always reliable but a reliable test is not necessarily valid. Discuss.test is not necessarily valid. Discuss.