Question

A health psychologist seeks to predict compliance with medical prescriptions using a self-report measure of methodicalness (M) and a health knowledge test (HK), the latter scored as pass (1) / fail (0). Out of 120 participants available at the study's outset, only 30 are still involved at the 6-month point, when compliance (C) is assessed. Information on all three measures and their interrelationships is provided below.

       Time 1   Time 2   Correlations/

       (N = 120)   (N = 30)   reliabilities*

       __________________   __________________   ______________________

   Measure   Range   Mean   SD   Mean   SD   M   HK   C

      

   Methodicalness   3 – 20   12.00   4.00   15.00   3.30   .82

   Health Knowledge   0 – 1   .50   .50   .80   .40   .32   .62

   Compliance   6 – 15           11.00   1.80   .40   .28   .72

      

   *Reliabilities are shown in bold.

a) What would be the observed criterion validity of the M scale if the full range of M scores from time 1 was available for correlation with prescription compliance? Also, what explains the drop in SD from T1 to T2? (3 pts.)

Answer 1