Substituing Supplementary Subtests for Core Subtests on Reliability of WISC–IV Indexes and Full Scale IQ

The effects of replacing core subtests with supplementary subtests on composite score reliabilities were evaluated for the WISC–IV Indexes and Full Scale IQ. When Wechsler's guidelines are followed, i.e., only one substitution for each Index; no more than two substitutions from different Indexes when assessing the Full Scale IQ, summary score reliabilities remain high, and measurement error, as defined by confidence intervals around obtained scores, never increases by more than 1 index score point. In three instances, substitution of a supplementary subtest for a core subtest actually increased the reliabilities and decreased the amount of associated measurement error.