Intellectual disability and its relationship to autism spectrum disorders.
Autism and intellectual disability often co-occur and shape each other’s severity, so test adaptively and plan for both domains.
01Research in Context
What this study did
Matson et al. (2009) pulled together every paper they could find on autism and intellectual disability.
They asked: how often do the two labels travel together, and does one make the other worse?
No new kids were tested; the team simply mapped what earlier work had shown.
What they found
The review shows the conditions show up in the same person far more than chance would allow.
When both are present, each can magnify the other’s traits, but exact numbers were not given.
The authors end by listing big holes in the research base.
How this fits with other research
Thurm et al. (2020) picks up the measurement thread and warns that classic IQ tools miss small gains.
They advise out-of-age testing or fresh metrics, moving the conversation forward from the 2009 gaps.
Ganz et al. (2004) seems to clash: psychiatric signs drop as ID deepens, yet L et al. say severity links with more autism traits.
The difference is angle: B et al. counted DSM psychiatric symptoms, while L et al. tracked broader developmental overlap.
Halladay (2025) gives you a fix today: use Vineland-3 and person-ability scores instead of old IQ floors.
Why it matters
You will meet many clients who carry both labels.
Expect complex profiles, and do not trust a single IQ number to guide goals.
Pull adaptive data, watch for floor effects, and plan interventions that tackle both social and cognitive pieces at once.
Want CEUs on This Topic?
The ABA Clubhouse has 60+ free CEUs — live every Wednesday. Ethics, supervision & clinical topics.
Join Free →Run the Vineland-3 on your next dual-diagnosed client and set goals in the lowest adaptive subdomain.
02At a glance
03Original abstract
Intellectual disability (ID) and autism spectrum disorders (ASDs) covary at very high rates. Similarly, greater severity of one of these two disorders appears to have effects on the other disorder on a host of factors. A good deal of research has appeared on the topic with respect to nosology, prevalence, adaptive functioning, challenging behaviors, and comorbid psychopathology. The purpose of this paper was to provide a critical review and status report on the research published on these topics. Current status and future directions for better understanding these two covarying disorders was reviewed along with a discussion of relevant strengths and weaknesses of the current body of research.
Research in developmental disabilities, 2009 · doi:10.1016/j.ridd.2009.06.003