Evaluation of the Wechsler Individual Achievement Test-Fourth Edition as a Measurement Instrument.

The Wechsler Individual Achievement Test (WIAT-4) is the latest iteration of a popular instrument that psychologists employ to assess academic achievement. The WIAT-4 authors make both pragmatic and measurement claims about the instrument. The pragmatic claims involve being useful for identifying individuals in certain academic achievement-related groups (e.g., specific learning disability). The measurement claims are twofold: (a) the instrument's scores represent psychological attributes, and (b) scores transformed to standard score values have equal-interval properties. The WIAT-4 authors did not provide the evidence necessary to support the pragmatic claims in the technical manual, so we could not evaluate them. Thus, we limited our evaluation to the measurement claims for the composite scores. To do so, we used information in the technical manual along with some additional factor analyses. Support for the first measurement claim varies substantially across scores. Although none of the evidence is particularly strong, scores in mathematics and reading domains tend to have more support than the writing and total achievement scores. Support for the second claim was insufficient for all scores. Consequently, we recommend that psychologists wishing to interpret WIAT-4 composite scores limit those interpretations to just a few in the mathematics and reading domains. Second, psychologists should completely refrain from using any composite score in a way that requires equal-interval values (e.g., quantitative score comparisons). Neither of these recommendations necessarily disqualifies the scores from being useful for pragmatic purposes, but support for these uses will need to come from evidence not currently provided in the WIAT-4 technical manual.