External validation of the equivalence of two computational formulas for a WAIS-R seven-subtest short form

The usefulness of an abbreviated form of the Wechsler Adult Intelligence Scale-R (WAIS-R) has been noted by several researchers. A 7-subtest short form yielding estimates of Verbal, Performance, and Full Scale IQs (FSIQs) has shown good reliability and validity. Both weighted and prorated formulas have been used interchangeably to compute estimated IQs derived from this short form. The purpose of this study was to compare the equivalence of these formulas with the full WAIS-R in a mixed clinical sample. Results show that both formulas produce nearly identical results, with neither formula emerging as clearly superior over the other; validity coefficients for WAIS-R IQs ranged from .95 to .97. A very slight absolute advantage was noted for the prorated over the weighted formula in that it resulted in fewer IQ differences greater than 2 standard errors of measurement, fewer misclassifications of FSIQ, and stronger correlations with WAIS-R Verbal, Performance, and FSIQs.