Full scale IQ as mediator of practice effects: The rich get richer

Differential effects of practice over four administrations of the WAIS-R were examined as a function of Full Scale IQ at initial testing (N = 36). Twelve education-matched normal adults represented each of three groups: Low-Average (80—90), Average (95—105), and High-Average (110—120) Full Scale IQ. Participants were tested at 2-week intervals. Repeated measures analysis of variance indicated that Average and High-Average groups made greater gains across retest intervals than did the Low-Average group (p < .002). Across groups, gains were greater at the first retest than at the second or third retest (p < .001). A Scale × Time interaction indicated disproportionate gain in Performance IQ versus Verbal IQ, particularly at the first retest (p < .001). Previous exposure to the WAIS-R dramatically alters performance: Traditional interpretations regarding expected gain and profile analysis are not valid at retest.