Attention deficit hyperactivity disorder among adults with severe and profound mental retardation.

The team gave DSM-IV checklists and Conners scales to staff who knew 86 adults with severe or profound intellectual disability.

They wanted to see how many met full ADHD criteria, regardless of the person’s exact IQ or age.

Fifteen out of every 100 adults qualified for an ADHD diagnosis.

That rate is far higher than you see in the general population.

Wilmut et al. (2013) later asked the same question in adults with autism and found an even bigger one-third positive rate, showing ADHD risk climbs when social disability is added.

Bhaumik et al. (2008) screened Irish special-school children with ID and hit 56% elevated Conners scores, hinting that kids may look more impaired than adults or that teacher ratings inflate numbers.

Bigham et al. (2013) flags the inflation issue directly: once developmental age was counted, parent reports no longer predicted actual impulsivity, suggesting our 15% figure might shrink if we controlled for mental age.

Lancioni et al. (2009) looked at adults with only mild-borderline ID plus ADHD and found extra attention deficits on lab tasks, pointing out that cognitive testing—not just checklists—helps judge how real the ADHD is.

One in seven adults with severe ID already meet ADHD criteria, so add Conners or DSM-IV items to your intake packet.

If the person’s mental age is much lower than their years, back up checklist scores with direct attention tasks or you may over-diagnose.

Use the data to argue for smaller staff ratios, noise control, and structured schedules that help both ADHD and ID.