Prevalence of psychiatric disorders in New Zealand prisons: a national study

Objective: The paper describes the methodologies and results obtained on a large cohort of prison inmates in New Zealand who were screened for psychiatric disorder. Method: All women and remanded male inmates in New Zealand prisons, and a randomly selected cohort of 18% of sentenced male inmates were interviewed. Interviewers used the Composite International Diagnostic Interview - Automated to establish DSM-IV diagnoses, and the Personality Disorders Questionnaire to identify personality disorder. All prisons in New Zealand were visited. Results: The results indicate markedly elevated prevalence rates for major mental disorder in the prison population when compared with community samples. This is especially the case for substance misuse, psychotic disorders, major depression, bipolar disorder, obsessive-compulsive disorder and posttraumatic stress disorder. Of particular concern is not only the increased prevalence rates for schizophrenia and related disorders but also the high level of comorbidity with substance misuse disorders demonstrated by this group. While 80.8% of inmates diagnosed with bipolar disorder were receiving psychiatric treatment in the prison, only 46.4% of depressed inmates and 37% of those suffering from psychosis were receiving treatment. Maori inmates were grossly overrepresented in the remand, female and male sentenced inmate population compared with the general population. Conclusions: A significant increase in provision of mental health services is required to cope with the high number of mentally ill inmates. The level of need demonstrated by this study requires a level of service provision that is quite beyond the capacity of current forensic psychiatry services, Department of Corrections Psychological Services or the prison nursing and medical officers. The elevated rates of common mental disorders argues for the use of improved psychiatric screening instruments, improved assessment and treatment capacities in the prison and an increased number of forensic psychiatric inpatient facilities to care for those psychotic inmates who are too unwell to be treated in the prison.