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Validity

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

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Validity

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  1. 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?

  2. 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?

  3. 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

  4. 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

  5. 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

  6. 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.

  7. Criterion-Related Validity (cont.) • Predictive validity • Test given, criterion measured later • Ex. ACT & College GPA; employment test & job performance • Incremental validity

  8. 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

  9. Decision Theory • 4 outcomes

  10. Cut scores & Hit rates

  11. 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?

  12. 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

  13. 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

  14. Factor Analysis (cont.) • Methods of factor analysis • Exploratory • Correlation matrix • Factor matrix with loadings • Label factors • Used to develop or eliminate items or scales from composite scores

  15. Factor Analysis (cont.) • Confirmatory factor analysis • Goodness of fit • After test has been developed

  16. Validity & Bias • Bias: a factor inherent within a test that systematicallyprevents accurate, impartial measurement • Bias implies systematic, not random variation • Can you make equally valid predictions for different groups?

  17. Bias in Predictions • Questions of regression • Slope • Intercept • Error of estimate

  18. Slope Bias

  19. Intercept Bias

  20. Rating error • Leniency Error • Severity Error • Central Tendency Error • Halo Effect

  21. 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?

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