Performance Pattern Differences on Measures of Verbal Intelligence In Children with Autism Spectrum Disorders and Attention Deficit-Hyperactivity Disorder

     

Background: With current Autism Spectrum Disorder (ASD) diagnostic assessment tools being more sensitive than specific (Lord et al., 2000), it is often recommended that they be used as part of a broader evaluation to diagnose an ASD (Chawarska, Klin, Paul, & Volkmar, 2007). However, specific recommendations of additional tools useful in the screening or diagnosis of ASD are less available. Although not specifically designed for ASD diagnostic purposes, children with ASDs frequently undergo developmental/psychological evaluation including cognitive/intelligence assessment. Given the widespread use of cognitive measures (e.g., in schools, outpatient clinics), identification of a performance pattern specific to ASD could be useful for screening and further diagnostic evaluation referral purposes. To date, no such pattern has been identified.

Objectives : Performance patterns on verbal subtests from the Wechsler Intelligence Scale for Children-IV (WISC-IV) were compared between a clinically-referred sample of children with autism spectrum disorders (ASD) and attention deficit/hyperactivity disorder (ADHD).

Methods: Data used for this study were from a clinical registry housed at an outpatient clinic specializing in autism spectrum disorders that is part of a large urban children’s hospital.

Retrospective chart review was used to gather data, including demographic information (i.e., sex, age, handedness, parent education, medication history), diagnosis, and WISC-IV performance. Children ages 6-16 years with Verbal Comprehension Index (VCI) greater than a standard score of 70 from the WISC-IV were included in the study. Children were also included if their evaluation resulted in a clinical diagnosis of autism, Asperger’s disorder, PDD-NOS, or ADHD. The final sample included 55 children with ASD and 24 children with ADHD.  

Results: Independent samples t-test revealed significant differences between groups (ASD > ADHD) on the Similarities subtest (t_{(2, 77)}=2.3, p=.03); no differences were found between groups on the Vocabulary and Comprehension subtests or demographic variables (p > .05). Within groups, children with ADHD performed similarly across the three subtests; however, children with ASD demonstrated a distinct pattern of performance, where they obtained the highest scores on Similarities, followed by Vocabulary, and Comprehension. Specifically, only for the ASD group, paired samples t-tests revealed highly significant differences between performance on Similarities and Vocabulary (t_{(1, 54)}=5.2, p<.001), Similarities and Comprehension (t_{(1, 54)}=7.7, p<.001), and Vocabulary and Comprehension (t_{(1, 54} 3.9, p <.001).

Conclusions: For children with ASD, but not those with ADHD, results indicated significant differences in performance across verbal measures from the WISC-IV, such that performance on the Similarities subtest was the highest, followed by Vocabulary, with Comprehension as the lowest. These findings suggest that while children with ASD and ADHD may share behavioral characteristics (e.g., inattention, social difficulties), they share less similarities in cognitive profile. The core language formulation and social reasoning deficits that are unique to ASD are hypothesized to explain the differing pattern of performance. Uncovering this pattern unique to children with ASD in our sample is particularly notable given use of clinical comparison group (who shared behavioral features with the ASD group), thereby increasing clinical applicability.