Objectives: We aimed to determine whether the latest WISC version continues to underestimate autistic intelligence.
Methods: 26 autistic and 22 typically developing children (age 6-16 years) completed WISC-IV and RPM at two different times. Levels of performance were compared through inspecting percentiles derived from mean standard scores (WISC-IV) and from mean raw scores and ages (RPM) for each group. Parametric and nonparametric statistical comparisons were then conducted with individual percentiles. Similar results were obtained with all procedures.
Results: Typical children achieved similar percentile values on RPM (73rd percentile) and WISC-IV FSIQ (75th percentile). This was not the case for autistic children, who scored at the 61st percentile on RPM but only at the 21st percentile on WISC-IV. A significant difference between RPM and WISC-IV scores was found in the autistic group (p<.0005 in both parametric and nonparametric tests) but not in the typical group (p=.57 in parametric and p=.67 in nonparametric tests). In line with these results, the advantage of RPM over WISC-IV FSIQ was significantly greater for autistic than for typical children. Five autistic children, but no typical children, obtained RPM scores over 50 percentile points higher than their WISC-IV scores. While three autistic children had standard scores below 70 on WISC-IV, the lowest autistic RPM score was at the 10th percentile (IQ-equivalent estimate 81). The rest of the autistic children achieved RPM percentile scores of 18 or higher, with estimated RPM IQ-equivalents over 85. With respect to WISC-IV index scores, autistic children attained a mean Verbal Comprehension Index standard score of 84.6, compared to a mean PRI score of 104, which in turn was similar to their estimated RPM IQ-equivalent score.
Conclusions: Our results are consistent with and add to existing findings that Wechsler FSIQ significantly underestimates autistic intelligence. Given what is known about RPM as a complex test of fluid and general intelligence, our results also further challenge the notion that autistic strengths are at best a collection of simple, isolated, and low-level perceptual abilities. Finally, our results provide preliminary evidence that the WISC-IV PRI index score may better estimate autistic intelligence than WISC-IV FSIQ. These findings merit attention in both research and clinical practice.
See more of: Clinical Phenotype
See more of: Symptoms, Diagnosis & Phenotype