Test-retest stability of the WAIS-R in a clinical sample

This study assessed WAIS-R test-retest stability for a sample of 21 psychiatric and neurological patients. The test-retest interval ranged from 2 weeks to 144 weeks, with a mean of 38 weeks. Subtest stability coefficients were highly significant; only Similarities, r(19) = .45, p less than .05, fell below a correlation of .74. The Verbal, Performance, and Full Scale IQs yielded highly significant stability coefficients (.79, .88, and .86). Nevertheless, the range of gain or loss for any single individual was comparatively large. On the Full Scale IQ, 18 of 21 (86%) subjects showed changes of 3 points or more, and 8 of 21 (38%) actually changed IQ classifications. Gain or loss in total score was unrelated to initial level of brightness on the Full Scale, age at initial testing, or days between examinations. Conversely, gain or loss on the Full Scale was associated strongly with years of education, r(19) = .55, p less than .01. When the sample was divided into brain-damaged and psychiatric subgroups, the difference in retest gain on the Full Scale IQ was nonsignificant.