Intellectual disability in young people in custody in New South Wales, Australia – prevalence and markers

Background Intellectual disability (ID) is known to be more common in incarcerated groups, especially incarcerated youth. Aboriginal young people have higher rates of ID, and make up half of all youth in juvenile custody in New South Wales (NSW), Australia. We aimed to describe the prevalence of possible ID and borderline intellectual functioning (BIF) in young people in NSW custody, and to describe the association between possible ID and Aboriginality after adjusting for the inequalities in social disadvantage. Methods Baseline study of all youth in NSW Custodial Centres between August and October 2009, with 18-month follow-up. Using Wechsler Intelligence Scale for Children – Fourth Edition (WISC-IV) and Wechsler Adult Intelligence Scale – Fourth Edition (WAIS-IV) cognitive assessments, possible ID was defined as Extremely Low Intellectual Quotient range (Full Scale Intellectual Quotient, FSIQ < 70), and possible BIF was defined as Borderline IQ range (FSIQ < 80). Risk factors for possible ID and BIF included age, gender, Aboriginality, socio-economic disadvantage, offending history and psychological disorders. Results N = 295 (65%) of all young people in NSW custody completed cognitive and psychological assessments (87% male, 50% Aboriginal, average age 17 years). Almost one half (45.8%) of young people had borderline or lower intellectual functioning (by IQ assessment), and 14% had an IQ in the extremely low range (FSIQ < 70), indicating a possible ID. Aboriginal participants were three times more likely than non-Aboriginal participants to have a possible ID, but after accounting for the excess disadvantage in the Aboriginal group, Aboriginality was no longer a marker of ID. Incarceration from a young age and psychosis were significantly associated with possible ID in Aboriginal participants, compared with Aboriginal participants first incarcerated at a later age, and Aboriginal participants without psychosis. Conclusion The inequalities in criminal justice between Aboriginal and non-Aboriginal youth may exacerbate or contribute to the intellectual impairment of those incarcerated from a young age. Aboriginal young people with psychosis are also at high risk of cognitive impairments that might indicate a possible co-morbid ID, and these patients should be diverted at court into community assessment services, rather than incarcerated. These results highlight a need for better and earlier identification of young people (particularly Aboriginal youth) at risk of ID and other co-morbidities in the juvenile justice system.