National Study of Psychiatric Morbidity in NZ Prisons

An investigation into the prevalence of psychiatric disorders among New Zealand inmates. (1999)

Executive Summary


During 1997 and 1998 the Department of Corrections commissioned a national study of the prevalence of mental illness among prison inmates. The research was co-sponsored by the Ministries of Health and Justice.

The study was developed and conducted with as full a cross-cultural validation as possible. The researchers received excellent cooperation from prison management, staff and inmates. The overall response rate was 80 percent, which is highly satisfactory.

Informed consent was obtained for researchers to obtain socio-demographic statistics. Ethnicity, marital status, living circumstances, usual occupation and education levels were examined, as was present and past treatment for mental health problems.


The identification and treatment of mentally ill persons within the prison system has posed difficulties for both Corrections and Health personnel. The first Mason Report (Mason et al, 1988) recommended the establishment of Regional Forensic Psychiatry Services to provide care to prisoners, both within prison and on transfer to hospital if necessary.

In the ten years that have elapsed since the Mason Report, six Regional Forensic Psychiatry Services have been established. These Services provide inpatient psychiatric care, community follow-up, liaison and secondary consultation to general mental health services, prisons and court liaison services.

However, concerns continued about the mental health status of inmates, particularly arising from suicides. But no research on the incidence of mental disorders had ever been undertaken.

In 1995 the Department commissioned a pilot study on the mental health of inmates in Christchurch prisons. The purpose of this pilot study was to establish a methodology for a possible national study.

Results were reported to the Department of Corrections and the Ministries of Health and Justice in 1996. Inmates were assessed for two types of prevalence: first, whether they had suffered the particular disorder in the last month; and secondly, whether they had suffered the particular disorder ever in their lives. These are referred to as the "one-month" and "life-time" prevalence rates. These rates were then compared with community samples for the same disorders. [Wells et al, (1989); Oakley-Browne et al (1989).]

National Study Commissioned

The Canterbury Pilot Study indicated the existence of a large number of psychiatrically disturbed individuals within the prison system. This was of significant concern to both Mental Health Services and the Department of Corrections.

However, the size and nature of the incidence of mental disorder amongst the national prison population remained unquantified.

Therefore a comprehensive study of psychiatric morbidity in the prison population was commissioned. Auckland UniServices Limited, a wholly owned company of The University of Auckland, set up a research team of forensic psychiatry specialists, headed by Dr A I F (Sandy) Simpson and Dr Phil Brinded.

The objective of the study was to interview all female inmates, all male remand inmates and 15 percent of sentenced male inmates for an approximate sample size of 1300 from a total population of approximately 5,500. The overall response rate was 80 percent. All prisons were sampled. Informed consent was obtained from each inmate and concise demographic data was also collected. Interviews were conducted from October 1997 to June 1998.

Socio-Demographic Structure

The National Study population does not differ significantly from the most recent prison census data in terms of age, ethnicity, security status and offence characteristics. This gives grounds for confidence that the study group is representative of the current prison population.

Approximately half of inmates identify themselves as Maori, highest amongst women inmates. 32.7 percent of women are pakeha, and 11.7 percent 'other'. There are few women of Pacific origin but at least 8 percent of the male population are of Pacific origin. For sentenced men, 32.3 percent are pakeha and for remand men, 28.2 percent.

Along with marital status, living circumstances and usual occupation, inmates were asked to define the highest level of education they had received. Whilst two-thirds of all groups received some secondary school education, only 19.9 percent of women, 19.1 percent of remand men and 16.4 percent of sentenced men completed secondary education. This is approximately one fifth of the population. Nine percent went on to some form of tertiary education, more usually technical institute based than university. The three study populations showed great similarity in their educational achievement.

Past and Present Treatment for Mental Health Problems

All inmates were asked whether they had received treatment for mental health problems prior to, and since being in, prison. Just over half the women and remand men had never received treatment prior to entering prison, whilst 68.8 percent of the sentenced men had received no prior treatment.

Of those who had received prior treatment, the majority was from a primary health care or community agency only. Out-patient specialist care had been received previously by 9.9 percent of the women, 7.8 percent of remand men and 6.4 percent of the sentenced men. In-patient care had been received previously by the same percentage of women (9.9 percent), 15.3 percent of remand men, and 9.9 percent of the sentenced men.

Treatment for mental health problems within prison was examined. Women reported receiving slightly more treatment for mental health problems from health staff working in prison, especially from nursing staff, although fewer (one woman only as opposed to 2 percent of the men) had at some stage been transferred to a forensic psychiatry unit. Of the male samples, fewer in total had been seen for a mental health problem but not unexpectedly, more had been in special prison units and equivalent numbers of the sentenced men (20.8 percent) had been seen by a psychologist or psychiatrist. Approximately 2 percent had been transferred to a forensic psychiatric facility at some time in the past.

Treatment for alcohol and drug related problems in prison was enquired about and showed that a high proportion (42.7 percent) of the sentenced male inmates reported receiving such care at some point, compared with 20.8 percent of remand men and 22.2 percent of women inmates.

Current provision of medication to inmates for mental health problems reported 29.2 percent of women, 10.6 percent of remand male and 8.3 percent of sentenced male inmates receiving such medication.

Key Findings of the National Study

The results indicate a significantly higher rate of mental disorder than that in the community. This is particularly so for schizophrenia, for bipolar disorder, for major depression, for obsessive compulsive disorder and for post traumatic stress disorder. All these conditions are associated with high levels of distress and disability, especially during the acute phases of these illnesses.

The National Study also revealed that nearly 60 percent of all inmates have at least one major personality disorder. [page 45]

The National Study estimates that all inmates who have a current diagnosis of schizophrenia or a related disorder and bipolar disorder will require active psychiatric treatment and of those, 135 will require inpatient treatment. The life-time and one-month prevalence for these disorders is significantly higher than in the community. Of those inmates in the acute phase of these disorders, 30.6 percent are currently receiving mental health medication.

Two anxiety disorders, obsessive compulsive disorder (OCD) and post traumatic stress disorder (PTSD), were found to be more commonly represented than expected. The study found that lifetime prevalence of PTSD for women inmates was 37 percent and one-month prevalence was 16 percent. Community sample lifetime prevalence is 1.3 percent [Davidson et al. (1991), and Wells et al. (1989)]. The incidence of PTSD is grossly elevated relative to the community at large and is more in keeping with findings for high risk populations such as victims of criminal offences and combat veterans.

One quarter of all inmates has suffered a major depressive disorder. Inmates currently suffering an episode of major depression show as 11.1 percent of women, 10 percent of remand men, and 5.9 percent of sentenced men. The lifetime prevalence rates are 32.1 percent for women, 20.6 percent for remand, and 22.6 percent for sentenced men. These rates are twice as high as the community sample.

The National Study also revealed that 90 percent of those with major mental disorders also had a substance abuse disorder. Of the total prison population, 89.4 percent have a current substance abuse or dependence diagnosis; 35 percent of these inmates have received treatment for the abuse disorder since they have been in prison.

Substance abuse disorders are known to contribute to re-offending amongst offender populations. Substance abuse also leads to poorer prognosis of people with mental disorders.

Key Recommendations of the National Study

Schizophrenia & related disorders / Bipolar disorders

  • 'It is recognised that a significant increase in mental health provision is necessary for this group of people. This will involve increased provision of primary medical, psychiatric clinics and inpatient beds to address this unmet need. Ideal treatment would be assessment and treatment in prison by psychiatrists and nursing staff from regional forensic services, in liaison with prison health staff, for all these inmates, and probable hospital admission for, perhaps, the majority of them.'  [page 52]
  • It is noted that if the Gunn's group rate of need is utilised, then 'approximately 135 [inmates] would require hospital transfer, … but it should be remembered that these people are in addition to all inmates currently being treated in hospital at the time of the study.'  [page 52]

Major Depression, OCD, PTSD

  • 'These inmates require detection, assessment and treatment planning. This could be performed by primary medical staff, psychologist or nursing staff and referral, as appropriate, for psychiatric evaluation. Some of those with major depression will require inpatient care. Many should receive ongoing therapy which may be psychological or by medication.' [page 52]

Substance misuse disorders

  • Because of the elevated rate of substance misuse disorders (89.4%), and because one-third of all those inmates also suffer from a range of other mental disorders, there is a clear need for policy to address these issues.
  • '… the very high rate of such disorders suggests a policy of exposing all inmates to some degree of basic drug and alcohol education, with a mechanism for identifying at least those with substance dependence disorders (about half of all those with misuse diagnoses.).'  [page 53]


  • The National Study indicates the need for 'a level of service provision that is quite beyond the capacity of current forensic psychiatric services, Department of Corrections Psychological Services or prison nursing and medical officers. The high rates of the common disorders argue for the use of screening techniques which can be followed up with formal assessment if a problem is identified. The same issues arise for substance misuse disorders.'  [page 53].
  • The study was developed and conducted with as full a cross-cultural validation as possible. Maori were consulted at a number of points during the development of the study design, interview process and, at times, with interviewers themselves.

    'There is a clear imperative to ensure that any increase in service provision has Maori centrally involved with the development of such services, as envisaged in the Mason Report.' [page 53]
  • We are confident that the sample gained is representative of all inmates. The National Study demonstrates that a significant number of inmates suffer elevated morbidity from a range of psychiatric disorders.


Schizophrenia and related disorders (schizophreniform, delusional, schizoaffective disorders)
Schizophrenia, schizo affective disorder, schizophreniform disorder and delusional disorder are all major psychotic disorders which share many clinical features in common and share genetic, causative and treatment implications. They differ in terms of their time course (schizophreniform disorder is the same as schizophrenia except that it is of shorter duration) or clinical features (schizoaffective disorder differs from schizophrenia only in having mood disorder components as well psychotic features, and delusional disorder has many similar features to schizophrenia except that the presentation is primarily of delusional beliefs). These are major mental disorders that cause severe disruption to an inmate?s thought process. They are often lifelong illnesses requiring long term psychiatric treatment.

Bipolar affective disorders
These are major mental illnesses where the person suffers extreme mood swings from mania (high energy, no sleep, expansive ideas etc) to depression. These mood swings cause severe disruption to the person's functioning and require ongoing psychiatric treatment. This is usually a life-long illness.

Major depression
This is a major mental illness where persons experience a profound drop in mood, energy and initiative, often becoming so distressed as to consider or attempt suicide. It is a treatable disorder but episodes of depression are often recurrent throughout life. The potentially serious consequences of untreated depression and the success of treatment make this an important mental illness to identify.

Obsessive compulsive disorder
This is a condition of recurrent intrusive patterns of thoughts and/or behaviour (such as continual handwashing and obsessional checking routines), and can be very debilitating and require medical intervention.

Post traumatic stress disorder (PTSD)
This is an anxiety disorder that follows the person experiencing a particularly traumatic (usually life threatening) event. Patients with PTSD can suffer quite severe distress and will often require psychiatric or psychological treatment.

Personality disorders
These are pervasive patterns of thinking, feeling, interacting and behaving with the environment and others around them. Treatment knowledge for such conditions is limited and management is usually confined to behavioural management and attempts to help patients gain insight into their condition and learn to ameliorate their own behaviour.

References quoted within this Summary

Davidson J, Hughes D, Blazer D and George L (1991)

Post traumatic stress disorder in the community: an epidemiological study. Psychological Medicine. 21: 713-721.

Mason K et al, (1988)

Report of the Committee of Inquiry into procedures in certain psychiatric hospitals in relation to admission, discharge or release on leave of certain classes of patients. Wellington, Government Printer

Oakley-Browne M et al (1989)

Christchurch Psychiatric Epidemiology Study, Part 2: Six months and other period prevalence of specific psychiatric disorders. Austr NZ J Psychiatry. 23: 327-340.

Wells J E et al (1989)

Christchurch Psychiatric Epidemiology Study, Part 1: Methodology and Lifetime Prevalence for Specific Psychiatric Disorders. Austr NZ J Psychiatry. 23: 315-326