The reliability and stability of the Full Scale IQ scores of retarded adolescents and young adults on 3 Wechsler Scales were measured. For mean retest intervals ranging from about 1.75 to 3.5 years, intratest reliability and constancy were reasonably good, although a significant rise in mean IQ was found for the WISC-R retest. Intertest reliability was also inadequate, but intertest constancy was not. The mean WISC-R IQ was significantly lower than the mean WISC IQ, and both were dramatically lower than the mean WAIS IQ. Comparisons are made with previous findings and implications of these results are discussed.The periodic retesting of large numbers of individuals in residential facilities provides the opportunity for analysis of the stability and comparability of standardized intelligence tests for specified populations. The present study assesses the constancy and intertest correlations of the Full Scale IQ scores of retarded individuals who have been or who now are residents at the Johnstone Center, an open, relatively short-term residential facility housing primarily mildly and moderately retarded adolescents and young adults. This population provides a particularly severe test of the reliability of the IQ score, as most of the residents come from broken homes and are frequently under stress, particularly when they are tested shortly after admission.
METHODThe records of all students now or recently at Johnstone were searched. Each of the Wechsler Full Scale IQ scores of each student who was tested more than once, either on the same Wechsler Scale or on a different Wechsler Scale, was recorded.