This study examined the effect of the revisions to the WPPSI-III on the level of receptive and expressive language demands of the test. Language demands were explored in relation to associated IQ scores. Service eligibility was also investigated vis a vis IQ scores. In addition, the correspondence between the nature of the revisions to the WPPSI-III, and the potential changes in the relationship between the WPPSI-III and the PLS-4 was investigated. The overall sample consisted of 221 preschool children, between the ages of 2 years, 7 months and 5 years, 3 months, who were referred for a comprehensive special education evaluation. WPPSI-III scores were obtained for 110 children, 76 of whom also had PLS-4 scores. WPPSI-R scores were obtained for 110 children, 82 of whom also had PLS-3 scores. An attempt was made to equate the two groups with regard to important demographic variables, such as age, sex, ethnicity, and reason for referral. Receptive and expressive language demands of both the WPPSI-III and the WPPSI-R were evaluated by two independent raters via a researcher created likert scale for use in categorizing relative language demands.
Results revealed that the WPPSI-III and the WPPSI-R differed significantly with regard to receptive and expressive language demands. The reduced language demands on the WPPSI-III, in turn, impacted IQ scores, as the children in this at-risk population who were evaluated with the WPPSI-III had significantly higher Verbal IQ scores than those who were assessed with the WPPSI-R. There was no significant difference between the correlations of the WPPSI-III and the PLS-4, and those of the WPPSI-R and the PLS-3.
One important implication of this study is that school and clinical psychologists must be very careful when utilizing an updated version of an intelligence test. Measuring cognitive functioning can become problematic during any period of transition from wide use of an established test to a revision, and this appears to be true for the WPPSI-III. The direction of the difference between the mean intelligence scores on the old and new instruments must be considered. Children in this at-risk population demonstrated higher Verbal IQ scores on the WPPSI-III, which is in the opposite direction of what would be predicted by the Flynn Effect. For this reason, psychologists can not necessarily give equal weight to IQ scores from the old and new versions of a test. Caution should be exercised with regard to service recommendation and considering reclassification. A balanced consideration of other diagnostic information will be most effective in preventing inappropriate discontinuance of services, especially in light of the reduced language demands on the WPPSI-III.
