Longitudinal Stability of Intellectual Functioning in Autism Spectrum Disorder: From Age 3 Through Mid-adulthood.
Molly B D Prigge, Erin D Bigler, Nicholas Lange and 13 others
PMID 34677753WHAT IT FOUND
In autism, group IQ scores rise from childhood to adulthood, but individual scores vary widely.
Verbal and working memory stabilize by adulthood, while non-verbal scores keep rising. Do not rely on a single childhood IQ score to predict adult function.
Key findings
01Group mean IQ scores in the autism cohort increased significantly with age, particularly for Full Scale and Verbal IQ, starting lower than the control group in childhood.
02Verbal and working memory scores showed the greatest stability within individuals by early adulthood, suggesting a single adult test may be sufficient for these domains.
03Despite group-level stability, over 50% of individuals with autism had at least one IQ score fall outside the 95% confidence interval of their initial score, even after age 16.
STILL TO COME
How it was doneWhat they foundWhat it means for PTsWhat it means for OTsWhat it means for SLPs
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What it does not show
The study focused on cognitively able (IQ ≥ 70), verbally able, and predominantly male participants, so findings may not apply to females or those with intellectual disability. Different IQ tests were used across ages (e.g., Mullen/DAS in childhood, Wechsler in adulthood), which may contribute to apparent variability or instability in scores. The typically developing control group was smaller in early childhood and not IQ-matched to the autism group, limiting comparisons in that age range. The study did not track social, economic, or environmental factors that could influence cognitive development and test performance.
Declared interests
Funding was provided by the National Institute of Mental Health and the National Institute of Child Health and Human Development. No commercial conflicts of interest were reported.
The easy way to misread this
Do not interpret the group-level increase in IQ as evidence that autism causes cognitive improvement or that early intervention is unnecessary. The rise is partly due to regression to the mean and test changes, and individual variability is high, meaning many individuals do not show this pattern.