Discrepancy on Stanford Binet Intelligence Scales-Fifth Edition in Adults with ASD in Mid-Adulthood

Background: Intelligence (IQ) tests are frequently used to evaluate cognitive functioning in persons with ASD. Studies show on the Stanford Binet Intelligence Scales-Fifth Edition (SB-5), children and adolescents with ASD exhibited higher nonverbal IQ skills compared to verbal IQ skills (Coolican et al., 2008; Matthews et al., 2015). It is unclear if these same discrepancies on the SB-5 are maintained through adulthood. It is important to understand the cognitive profile of adults with ASD to determine relative strengths and weaknesses as well as intervention and treatment strategies that may be appropriate for adults with ASD.

Objectives: The goal of this study was to evaluate discrepancy in verbal and nonverbal IQ in adults with ASD using the SB-5. This included evaluating discrepancies on the five individual subscales of the SB-5 (Fluid Reasoning, Knowledge, Quantitative Reasoning, Visual Spatial, and Working Memory).

Methods: Fifty-five adults with ASD (M age=37.12 years, SD=6.85 years) who were diagnosed as children completed adult evaluations of adaptive behavior, ASD symptoms, and IQ. Participants that received the lowest possible score on the SB-5 were excluded from analyses (n=16) due to limited ability to evaluate discrepancies of standard scores. The final sample of participants included 39 adults with ASD (M age=35.55 years, SD=6.06 years, range=26-49 years). Overall verbal and nonverbal IQ scores in addition to verbal and nonverbal subscales of the SB-5 were compared using pairwise comparison.

Results: Results indicated no significant differences in overall nonverbal and verbal IQ standard scores [t(38)=.23,p=.82]. However, when evaluating differences between nonverbal and verbal subscales, results are more complex. Using the t-scores for each subscale, verbal abilities were significantly higher than nonverbal abilities for the Knowledge and Working Memory subscales (p=.002 and p=.03, respectively). In contrast, nonverbal abilities were significantly higher than verbal abilities on the Quantitative Reasoning and Visual Spatial subscales (p=.005 and p=.001, respectively). (See Table 1).

Conclusions: Adults with ASD present with complex cognitive profiles that may not be represented by evaluating overall IQ scores alone. Rather, there are significant discrepancies on the subscale level that suggest more variable skills. However, clinical significance of these discrepancies must be considered given that all mean verbal and nonverbal subscales are within 1 standard deviation of each other. In addition, given the small sample size of this study, results must be interpreted with caution. Although more research is needed, this study is one of the first of its kind to examine these differences in adults with ASD across mid-adulthood and exemplifies the complexity and variability in these skills for adults with ASD.