Prevalence of intellectual disability in northern Sydney adults.
In northern Sydney, only 3 in 1,000 adults have ID, but justice settings show rates ten times higher.
01Research in Context
What this study did
The team counted adults with intellectual disability in northern Sydney. They used IQ below 70 as the cut-off.
Everyone aged 20-50 living in the area was included. Hospital and care-home records helped find cases.
What they found
About 3 in every 1,000 adults had ID. One-third of those cases were Down syndrome.
Roughly 4 out of 10 adults with ID still lived in large institutions.
How this fits with other research
Koegel et al. (2014) looked at youth in NSW custody two decades later. They found almost half scored in the borderline or lower IQ range. The jail rate is far higher than the 3 per 1,000 seen in the general public.
Herrington (2009) saw the same jump in young male prisoners. One in nine had borderline ID alone. Together the papers show the justice system holds a big slice of the ID population.
Smith et al. (2010) and Plant et al. (2007) used the same head-count method in Norway and the Netherlands. Their numbers line up with Sydney’s, giving confidence that 3-7 per 1,000 is the true community rate.
Why it matters
If you work with adults, expect roughly three service users with ID for every thousand people in your catchment. Plan housing and day programs knowing that many may still come from institutional settings. When you serve teens or justice-involved youth, flip the lens: screen every new client, because prevalence there jumps to nearly 50 percent.
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02At a glance
03Original abstract
The prevalence of intellectual disability, defined as IQ < 70, was determined in a population of adults aged 20-50 years who lived in the northern suburbs of Sydney, Australia. Case finding was carried out in the community, and all those ascertained were interviewed and psychometrically assessed. The overall prevalence was 3.31 per thousand with severe intellectual disability (IQ < 55) 2.19 per thousand and mild (IQ 56-70) 1.12 per thousand. Down's syndrome had a frequency of 0.96 per thousand. Thirty-eight per cent of the total group were living in institutional care.
Journal of intellectual disability research : JIDR, 1996 · doi:10.1046/j.1365-2788.1996.769769.x