We thank Russell and House for raising an important issue that we lacked space to discuss in our paper.1 Although we noted that ‘practices may not identify all [intellectual disability] ID individuals, especially those with mild ID’, it was not our intention to underestimate this difficult task.
Adults with ID not known to primary care in England have been described as a ‘hidden majority’, due to administrative health systems failing to detect a large proportion of mild and moderate ID.2 Large discrepancies have been seen between the administrative prevalence of mild or moderate ID identified in school-age children compared with adults from primary care registers (the ‘transition cliff’2), and Public Health England has estimated that 2.17% of the English adult population may have ID.3
A meta-analysis estimated global ID prevalence at 1.0%,4 falling to 0.5% when only adults were considered. Our study of adults in England estimated a prevalence of 0.54%,1 similar to a recent Scottish study (0.56%).5 Prevalence rates in adults calculated using QOF registers have stabilised around 0.5%,6 so a true prevalence of 2.0%, implies 3/4 patients with ID are not on QOF registers. In our data, only 8% of practices had a prevalence >1.0%, so although ID coding is highly variable across practices, any potential under-recording of ID must be consistent across them.
In our data, among those with severity recorded, about 1 in 4 adults were classified as severe/profound, compared with 1 in 5 estimated known to schools in 2013.3 Assuming all severe/profound patients have been identified, and the under-recording is only of mild/moderate ID, then 2% prevalence would result in only 7% (1 in 15) of our patients having severe/profound ID, much lower than 1 in 5.
Finally, the implications for any under-recording in our study would be that our comparisons with the general population are exaggerated, as we assume that ID patients with chronic comorbidities are more likely to be known to primary care, presumably having their ID recorded as a result. However, our central message of improving continuity of care and offering longer appointment times is not changed. Nor should it detract from efforts to better collect and identify ID among adults.7
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