Classical Test Theory Goal of testing is to identify subject’s “true score” on a given attribute. Classical Test Theory says… Test Score=True Score+Error of Measurement Goal of test developers is to minimize this!
Sources of Measurement Error Where do these measurement errors come from? Item sampling error Internal consistency error Time sampling error Random error
Testing How do psychologists know how well their test is measuring a person’s true score? By assessing test reliability Test-Retest reliability Internal Consistency reliability Alternate or Parallel Form reliability Assesses Time sampling error Assesses Item sampling error Assesses Internal consistency error
Q9 Q10 Q17 Q18 Q9 1.0000 Q10.1829 1.0000 Q17.1888.5718 1.0000 Q18.1730.4031.5302 1.0000 Correlation Matrix Scale Scale Corrected Mean Variance Item- Squared Alpha if Item if Item Total Multiple if Item Deleted Deleted Correlation Correlation Deleted Q9 8.9250 8.4753.2220.0494.7513 Q10 9.4750 6.2272.5460.3452.5655 Q17 9.2875 5.3720.6160.4367.5080 Q18 9.1750 6.8804.5141.2999.5930 Reliability Coefficients 4 items Alpha =.6846 Standardized item alpha =.6749 I am carefree I am rarely overcome with worries I am not a worrier I rarely feel fearful or anxious Judging Internal Consistency Anxiety Scale Items 9. I am carefree 10. I am rarely overcome with worries 17. I am not a worrier 18. I rarely feel fearful or anxious
Testing How do psychologists know their test is measuring what they think it is measuring? By assessing test validity Content validity Criterion-related validity Construct validity
Assessing Construct Validity Convergent Construct Validity Our measure of extraversion should be correlated with things related to extraversion Divergent Construct Validity Our measure of extraversion should not be correlated with things unrelated to extraversion
Our measure of impatience should not be correlated with things unrelated to impatience. Correlations 1.000.857**-.085.857**1.000.039 -.085.0391.000 HEIGHT SHOE Impatience Scale HEIGHTSHOEEXTRA202 Correlation is significant at the 0.01 level (2-tailed). **. Assessing Construct Validity Convergent Construct Validity Our measure of impatience should be correlated with things related to impatience. Divergent Construct Validity Correlations 1.000.275* *1.000 Impatience Scale ‘02 Impatience Scale ‘03 ‘02‘03 Correlation is significant at the 0.05 level (2-tailed). *.
Testing Utility of Psychological Tests Reliability Alternate or Parallel Form Internal Consistency Test-Retest Validity Content Criterion-Related Construct