Prevalence of mental illness among Aboriginal and Torres Strait Islander people in Queensland prisons

Aboriginal and Torres Strait Islander people are 14 times more likely to be incarcerated than non-Indigenous Australians and represent 26% of the custodial population,1 despite being less than 3% of the Australian population.2 There are complex links between incarceration, social adversity and poor mental health for Indigenous people.3-5 While it is recognised that the prevalence of mental disorder among the general prison population is much higher than in the community,6,7 knowledge about the prevalence of mental illness among Indigenous people in custody is limited.8 This is particularly disconcerting given that the report of the Royal Commission into Aboriginal Deaths in Custody,9 released two decades ago, highlighted the need to better understand the mental health of Indigenous Australians in custody.

A recent report on the general health of Aboriginal inmates5 suggested that the prevalence of mental disorder among Indigenous inmates was high. Similarly, the high rates of death by drug overdose and suicide,10,11 and of hospital admissions for severe mental illness in this group12 in the immediate postrelease period, support this premise. Although previous studies have pointed to a high prevalence of mental illness among Indigenous prisoners,8 many have suffered from ill defined sampling frames that jeopardise generalisability, a lack of systematic screening within these sampling frames, exclusive reliance on screening instruments to identify possible mental illness and, most importantly, a lack of cultural sensitivity in the conceptualisation of mental illness and study design and implementation.

The aim of our study was to estimate the prevalence of mental disorders (depressive, anxiety, psychotic and substance misuse disorders) among a large and representative sample of Indigenous prisoners. It employed systematic sampling and gold-standard assessment methods and, for the first time, introduced culturally sensitive methods of diagnosing psychotic illness in Indigenous prisoners.

On 30 June 2008, there were 5544 adults in Queensland prisons,18 of whom 1381 men and 116 women identified as Indigenous. In the six centres surveyed, there were 1036 Indigenous men and 88 Indigenous women.

Of the 487 men approached to participate in the study, 347 (71.3%) were interviewed, 92 declined to participate, 45 were released, transferred or not available, and three were judged too unwell to be seen due to mental illness. The mean age of male participants was 31.5 years (SD, 9.4) and of the male non-participants was 28.8 years (SD, 8.18); this difference was statistically significant (P = 0.03). Of the 88 women approached to participate in the study, 72 (81.2%) were interviewed, 10 declined to participate, five were either released or not available, and one was judged too unwell to be seen due to a physical illness. There was no statistically significant difference in the mean age of female participants (29.2 years; SD, 8.5) and non-participants (30.47 years; SD, 8.35) (P > 0.05).

Of the 419 individuals who participated in the study, all completed the questionnaire and were screened for psychosis; 396 (94.5%) of these individuals also completed the CIDI automated interviews for anxiety, depressive and substance misuse disorders (331 men and 65 women). Of the 23 individuals who did not complete the CIDI, six (three men and three women) were diagnosed with a psychotic disorder.

Among the Indigenous inmates sampled, most men and women were diagnosed with at least one mental disorder, whereas the 12-month prevalence of mental disorder among adults in the Australian community is estimated at 20%.15 Given the vast overrepresentation of Indigenous people in prison, their frequent transition between prison and the community, and the high prevalence estimates of mental disorder in this group, the consequences of inadequate health care in prison7,19 must inevitably affect Indigenous communities. The prevalence of depression and anxiety disorders, especially post-traumatic stress disorder, was high in this sample, and is similar to prevalence estimates of general prison populations,14 highlighting the critical need for adequate mental health services in prison settings.7 The high prevalence of diagnosed psychotic disorder, particularly among women, is of concern and is consistent with other Australian studies.14,20 Psychotic disorder is associated with significant morbidity21 and increased risk of reincarceration.22 These findings highlight a critical mental health need for these individuals, both in custody and during the transition back to their communities.

This study, like others before it,8 identified a high rate of substance use problems among Indigenous prisoners. However, most previous studies have relied exclusively on screening instruments to do this, whereas our study has, for the first time, robustly estimated the diagnostic prevalence of harmful levels of substance misuse and dependence among Indigenous prisoners. The National Indigenous Drug and Alcohol Committee recently highlighted the lack of opportunities that exist for Indigenous people to access appropriate treatment for these problems in custody.23 It suggested that, if available, culturally appropriate interventions are likely to be successful, and it provided clear recommendations about how to implement these services. Evaluation of such services, in a way that is both culturally sensitive and scientifically rigorous, is an essential next step.

Sampling is a challenge for any research with custodial populations, due to difficulties accessing all custodial centres and because of daily releases, transfers and receptions. However, given the centres that we sampled contained 75% of all Indigenous men and 90% of all Indigenous women in custody at that time, and the high recruitment fractions for both populations, it is likely that the risk of sampling bias was minimised. Similarly, the risk of recall bias is likely to have been reduced by using 12-month prevalence estimates for mental disorders. It is possible that such high estimates of psychotic disorder, particularly among women, might indicate measurement bias. However, given the comprehensive and culturally sensitive method used to make the diagnosis, we believe that these findings are accurate. Further, any measurement bias would be at least partially offset by likely underdetection of psychotic disorders, due to false-negative results on the psychosis screener and the loss from the sample of some individuals who screened positive but could not undergo diagnostic interviews due to their release.

The small age difference between participating and non-participating men (about 2.5 years) is unlikely to have substantially biased our prevalence estimates, given the size of the male sample and that the mean age of this sample (31.5 years) was similar to that of the total Indigenous male population in Queensland prisons at the time of the survey (30.6 years). A key strength of our research was the extensive consultation conducted with both Aboriginal and Torres Strait Islander communities and the involvement of Indigenous people in all aspects of the research process. Inevitably, cultural bias is a risk in this field of research. We aimed to ensure that any cultural bias or response bias was minimised through the use of a culturally informed research method and trained, culturally competent interviewers.

The information obtained from our research is crucial to the planning and implementation of adequate mental health services for Indigenous people in contact with and leaving the criminal justice system. For mental health services to be effective, they must be culturally capable, and accessible both in custody and in the community, with a focus on enabling continuity of care between the two. Such services can only be achieved through appropriate resourcing and stewardship. Their development is not only supported from a public health perspective, but also from human rights and ethical perspectives.24,25

While the marked over-representation of Indigenous people in Australian prisons remains a significant concern, prisons provide an opportunity for health care for a population who underaccess health care in the community.26 Although reducing the Indigenous incarceration rate remains a priority, improving the mental health of Indigenous Australians, including those who come into contact with the criminal justice system, is also important. Access to appropriate treatment may help prevent the “revolving door” of incarceration.

Our study, the first of its kind in Australia, provides an opportunity for service planning and policymaking to be based on reliable estimates of the nature, type and extent of mental disorder among Indigenous people in custody. In embracing the challenge of closing the Indigenous health gap, it is critical that the mental health problems of Indigenous people in custody be addressed.

2 Twelve-month prevalence of mental health disorder among Indigenous people in Queensland prisons, May–June 2008 (n = 396)*

* For comparability purposes, excludes the 23 participants who did not complete the Composite International Diagnostic Interview.