Validity

• Does test measure what it says it does?

• Is the test useful?

• Can a test be reliable, but not valid?

• Can a test be valid, but not reliable?

Types of validity

• Face validity– Important only so far as it doesn’t interfere with

an examinee’s willingness to cooperate.

• Content validity– How well does the test cover areas of content

that it should?– How adequately does it sample the universe of

behavior it was designed to assess?

Content validity (cont.)

• Panel of “experts”– Is the item/content essential?– Lawshe (1975) >50% of experts see skill as

essential

• Important for: – Achievement/classroom tests– Training program exams– Professional exams

Criterion-Related Validity

• How well does a test score relate to another score/variable of interest?– Correlate test with criterion

• Standard against which test is evaluated

• Concurrent

• Predictive

Criterion-Related Validity (cont.)

• Criterion should be– Reliable

• Reliability limits validity; can’t be valid if not reliable.

– Relevant

– Valid

– Uncontaminated• Criterion measure has been based in part on predictor measure

Criterion-Related Validity (cont.)

• Concurrent validity– Criterion immediately available– Present standing on a criterion

• Diagnosis, score on another test

– Used to predict the performance of new test takers or for people for whom the criterion isn’t available.

Criterion-Related Validity (cont.)

• Predictive validity– Test given, criterion measured later– Ex. ACT & College GPA; employment test &

job performance

• Incremental validity

Base Rate & Decision Theory

• Base rate: proportion of population who possess a certain trait, characteristic or attribute– % of EIU undergrads who graduate– % of African Americans with sickle cell anemia

• Base rate affects usefulness of tests

Decision Theory

• 4 outcomes

False rejections/negatives

Valid Acceptances/

Positives

Valid Rejections/

negatives

False Acceptances/

Positives

Cut scores & Hit rates

False rejections/negatives Valid Acceptances/

Positives

Valid Rejections/

negatives

False Acceptances/

Positives

Cut scores & Hit rates (cont.)

• Reciprocal relationship between # of false rejections and # of false acceptances

• Which is more acceptable: to limit the number accepted who shouldn’t be, or to minimize the # rejected who could be successful?

Construct Validity

• Construct:– Scientific idea hypothesized to explain behavior

– Postulated attribute of people, assumed to be reflected in test score

– Ex.: intelligence, self-esteem, motivation

• Construct validity: Does the test measure the construct?– Gives theoretical meaning to scores;

– Subsumes all other types of validity

Construct Validity (cont.)

• Convergent evidence/validity

• Divergent/discriminant evidence

• Factor analysis– Data reduction/simplification of complex

correlational matrices … to reveal major dimensions that underlie a set of items

– A factor is considered to be the construct that best represents relationships among variables

Factor Analysis (cont.)

• Methods of factor analysis– Exploratory

1. Correlation matrix

2. Factor matrix with loadings

3. Label factors

• Used to develop or eliminate items or scales from composite scores

Factor Analysis (cont.)

• Confirmatory factor analysis– Goodness of fit– After test has been developed

Validity & Bias

• Bias: a factor inherent within a test that systematically prevents accurate, impartial measurement– Bias implies systematic, not random variation

• Can you make equally valid predictions for different groups?

Bias in Predictions

• Questions of regression– Slope– Intercept– Error of estimate

Slope Bias

Bias & the DAS

60

80

100

120

140

75 85 100 115

General Conceptual Ability Scores

Word Reading Scores

Whites

Asian Americans

Linear (Whites)

Linear (AsianAmericans)

Intercept Bias

Bias & the DAS

0

20

40

60

80

100

120

140

1 2 3 4 5 6

General Conceptual Ability Scores

Basic Number Skills

Series1

Series2

Rating error

• Leniency Error

• Severity Error

• Central Tendency Error

• Halo Effect

Test Fairness

• Is the test used in an impartial, just, and equitable manner?

• Good tests Discriminate among individuals– Are group differences due to inadequate tests?– Is the test being used fairly?