Measuring intelligence in Autism and ADHD: Measurement invariance of the-Binet 5th edition and impact of subtest scatter on abbreviated IQ accuracy.

Scatter and heterogeneity in cognitive profiles is thought to be common in autism spectrum disorder (ASD), which may indicate differences in the construct of IQ. However, less research has investigated IQ scatter in attention-deficit/hyperactivity disorder (ADHD). Scatter is also thought to negatively impact the predictive validity of IQ summary scores, although there is research refuting this notion. Abbreviated IQ tests, such as the Stanford-Binet fifth edition (SB-5) abbreviated battery IQ (ABIQ), may be especially susceptible to the influence of scatter. We tested the measurement invariance of the SB-5 as well as the predictive validity of the ABIQ in predicting FSIQ in 1679 youth (21% female) ages 2-16 years with a clinical diagnosis of ASD or ADHD. Results indicated the SB-5 is measuring IQ the same way in ASD and ADHD. There were no differences between diagnostic groups in scatter between ABIQ (i.e., routing) subtests. Additionally, scatter was not related to dimensional autistic traits. Higher degree of scatter was associated with poorer predictive validity of the ABIQ and a higher likelihood of overestimating FSIQ, regardless of diagnosis. Overall, we found more similarities than differences between the ASD and ADHD groups. Our results show that the SB-5 ABIQ is generally a strong predictor of FSIQ in youth with neurodevelopmental disorders. However, the use of the SB-5 ABIQ in research and clinical applications, without consideration of scatter on routing subtests, is potentially problematic.