What Can the WISC-R Measure?

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Abstract
The WISC-R was investigated by using measures of profile (multivariate) reliability in order to determine its most reliable dimensions and the precision and similarity of the multivariate structure across age groups. Due to differences among the 11 age groups in both subscale reliabilities and true score covariance matrices, it was concluded that the precision of measurement differed across age groups. This finding was further supported by a comparison of canonical reliability coefficients and composites computed for each age group. However, exhaustive analyses of Varimax rotated profile dimensions indicated that the structure of the WISC-R subscales is rather stable across age groups, but the reliability of that structure differs systematically. A synthesis of the analyses indicated that (1) the WISC-R allows highly reliable comparisons of profile levels (Full-Scale IQ) at each age level; that (2) reasonably reliable comparisons of Verbal-Performance differences can be made at each age level; but that (3) for other comparisons, caution should be exercised because of age group differences and potentially high unreliability. Two strategies for the interpretation of WISC-R profiles, which take into account the above findings, are offered