Selection bias on intellectual ability in autism research: a cross-sectional review and meta-analysis.
Ginny Russell, William Mandy, Daisy Elliott and 3 others
PMID 30867896WHAT IT FOUND
Autism research samples were mostly people without intellectual disability, so evidence may not apply to autistic patients who also have ID.
Key findings
01Of 165 studies that reported IQ or ID data, 82% showed selection bias against intellectual disability, and an estimated 94% of autistic participants did not have ID.
0238% of included studies did not report ID status, and 91% of later citations generalised results from samples without ID to all people with autism.
03Only 2% of autistic participants in studies reporting language status were non- or minimally verbal.
STILL TO COME
How it was doneWhat they foundWhat it means for SLPs
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What it does not show
The sample was not all autism research; it came from selected high impact autism journals in 2016. The authors did not conduct a full systematic review because an initial scoping review produced 30,000 hits. Many studies did not report ID data, and the authors did not impute missing data. ID was classified mainly by IQ above or below 70, so the review could not examine severity within ID as a continuous measure. Some studies excluded participants with ID in ways that were not visible from title screening.
The easy way to misread this
Do not conclude that autism interventions do not work for people with ID. The review found these patients were underrepresented, so the evidence base for them is missing rather than negative.