Invisible populations: Who is missing from research in intellectual disability?
Most adults with IDD are off the service grid—go to barbershops, clinics, and churches to find them.
01Research in Context
What this study did
Rosencrans et al. (2021) looked at who gets left out of intellectual-disability research.
They wrote a narrative review that maps where the missing adults live and how to reach them.
The goal was to help teams build samples that truly mirror the IDD adult population.
What they found
About six in ten adults with IDD never touch formal disability services.
They go to primary-care clinics, churches, grocery stores, and social clubs instead.
If you only recruit through agencies, your study skips most of the people you want to understand.
How this fits with other research
Matson et al. (1994) first warned that language barriers, wary families, and low consent returns shrink IDD samples.
Margaret’s team shows the problem is still here, just bigger.
van der Miesen et al. (2024) counted UK health studies and found 78% lock the door on adults with IDD.
Brodeur et al. (2025) adds the gatekeeper layer: staff and carers decide who even hears about a study.
Together the papers trace a straight line—hidden people, locked doors, and gatekeepers holding the keys.
Why it matters
Next time you plan a study, list places where adults with IDD already spend time.
Ask barbers, grocers, pastors, and primary-care nurses to hand out your flyer.
Build plain-language consent and extra time for guardian approval.
Better samples mean better data—and rules that finally fit the whole IDD community, not just the easy-to-reach slice.
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02At a glance
03Original abstract
It is estimated that approximately 41% of adults with intellectual and developmental disability (IDD) are served through the developmental disabilities (DD) system in the US. The remaining 59% include individuals who meet diagnostic criteria but are not actively receiving paid services or may not be known to the DD system. Scholars have referred to this group as the "hidden majority." Very little is known about the health and well-being of these adults. It remains to be seen if the hidden majority is comparably susceptible to mental health difficulties, given how little is known about this population by DD systems. The purpose of this manuscript is to highlight where one may identify individuals belonging to this hidden population and how researchers might effectively recruit from this group so as to ensure more representative samples of all people with IDD.
Research in developmental disabilities, 2021 · doi:10.1016/j.ridd.2021.104117