Co-morbidity research - Part one

Jill Bowman

Principal Research Adviser, Department of Corrections

Author biography:

Jill joined the Department of Corrections’ Research and Analysis Team in 2010. She manages a variety of research and evaluation projects, and has a particular interest in desistance, employment outcomes of released prisoners, how probation officers work with offenders and the needs of female offenders. As well as working for Corrections, she volunteers at Arohata Prison, teaching quilting to the women in the Drug Treatment Unit.


A study conducted in New Zealand prisons in 1999 showed that up to 70 percent of prisoners have drug and/or alcohol problems, and a significant proportion have various mental health issues. However, that research didn’t consider the co-existence of mental health issues and drug/alcohol problems.

Overseas studies have identified significant rates of dual diagnosis, that is, the co-existence of substance misuse and mental health problems. A 2009 report in the United Kingdom suggested that dual diagnosis of prisoners should be the norm. However, it is acknowledged that dual diagnosis can be difficult, as the symptoms related to drug use and those related to mental health disorders can be confused. In addition, the symptoms related to drug taking or mental health disorders may combine and reinforce each other when they appear, making it difficult to distinguish between the two.

In 2014, Corrections successfully applied for funds from the Government’s Proceeds of Crime allocation under the Methamphetamine Action Plan to conduct a study into the prevalence of co-morbid mental health and substance abuse issues amongst prisoners. Offenders are screened for drug and alcohol issues and mental health problems on reception to prison but, if problems are indicated, further assessments are conducted separately and the conditions are treated in parallel or serially.

Identifying the actual extent and range of co-existing substance misuse and mental illness would enable the department to review and improve its screening, assessment and referral processes, and to make changes to treatment options as appropriate. This would ensure optimal treatment is provided to prisoners in response to their need, and that co-morbid substance abuse and mental health issues could be addressed in a more effective and integrated way.

Although the department already achieves success with its drug treatment programmes, integrated treatment of substance abuse and mental health disorders has the potential to further lower re-offending rates.

The study

The Department contracted two specialist providers to assist with the study. National Research Bureau Limited (NRB) interviewed the prisoners about their substance abuse and mental health history, and Craig Gear and Associates (CGA) is analysing the data and producing the final report.

Interviews commenced in March 2015 after the study had obtained ethics approval from the Health and Disability Ethics Committee.

Over 1,200 newly sentenced prisoners, who were aged 18 years or older and who were proficient in English, were interviewed for the research. This number provided a mix of males/females, age groups, ethnicities, offence types, sentence length, and repeat/first time offenders, enabling the results to be generalised to produce a comprehensive picture of co-morbid drug/alcohol and mental health issues across the entire New Zealand prisoner population. Although the preference was to interview prisoners who had been on sentence for less than one month, those who had been on sentence for between one and three months or who were remand convicted were also interviewed, if insufficient numbers of newly sentenced prisoners were available.

Initially prisoners for interview were drawn from ten prisons:

  • Auckland Region Women’s Corrections Facility
  • Auckland Prison
  • Waikeria Prison
  • Spring Hill Corrections Facility
  • Hawke’s Bay Regional Prison
  • Wanganui Prison
  • Rimutaka Prison
  • Christchurch Women’s Prison
  • Christchurch Men’s Prison
  • Otago Corrections Facility.

However, Invercargill Prison and Manawatu Prison were added in May, and Mt Eden Corrections Facility was included in June, when it became apparent that it would take longer than scheduled to interview the desired numbers of prisoners.

The study used two diagnostic tools, the World Health Organization World Mental Health Composite International Diagnostic Interview (WHO WMH-CIDI version 3.0) and the Personality Diagnostic Questionnaire-4+ (PDQ-4+). The latter was administered in lieu of the Personality Disorder module of the CIDI. Both tools are administered via the computer-assisted personal interviewing (CAPI) technique.

The CIDI was used in the 1999 New Zealand study and has also been used in prison populations in other countries, including Australia.

The CIDI is constructed in modules, each of which addresses a mental health disorder. The modules included for this study were:

During a three-day course, NRB interviewers were trained in the use of the CIDI by WHO-authorised trainers from the University of Tasmania, Australia. Trainers were trained on a fourth day so that they could educate additional interviewers as required.

Each prison identified staff to liaise with the interviewers, organise interview rooms, and to arrange for prisoners to be invited to take part in the study. Each prison was provided with a list of prisoners who were eligible for the study every week, and Corrections staff approached these prisoners and asked them to take part in a health survey. Prisoners were able to decline to participate at this stage (and at any subsequent time during the process). Those who agreed were taken to an interview room where they met the interviewer who explained the study to them. As well as providing information verbally, the interviewers gave the prisoners an information sheet on the research. Prisoners could take this background information away with them to consider further before they consented (or declined) to participate if they wished. Prisoners who agreed to take part in the study signed a consent form, after it had been discussed with them.

Interviews generally took between two and three hours to complete. Occasionally, because of prison routines, an interview could not be completed in one session and had to be resumed at a later time. While Corrections staff escorted prisoners to and from interviews, they did not sit in on the interviews.

Interviewers read questions aloud to prisoners and their answers were recorded on laptops. Cue cards were associated with some questions, and these were shown to prisoners to help them answer.

At the end of each interview, participants were advised to make known to the interviewer or to prison staff if they felt upset by the experience. Interviewers who believed the interview had caused distress to any prisoners also advised Corrections staff so they could be given appropriate support and follow-up.

Interviews were completed in mid-July. In total, 1,368 of the 1,557 prisoners who met the interviewer and had the research explained to them, agreed to take part in the study. However, not all of those completed the interviews.

All information from the interviews was aggregated and anonymised before it was sent to CGA for analysis. Corrections provided demographic and offending information to complement the interview data. This included age, gender, ethnicity, prison status at date of interview, index offence, number of previous custodial sentences, age at first custodial sentence, time spent in prison and, for other than remand convicted offenders, commencement date for this sentence and sentence length.

Results of the study

The results of the interviews are currently being analysed and a final report is being prepared. The report will provide information on the prevalence of mental disorders, anxiety disorders, mood disorders and substance disorders, as well as the co-existence of these disorders. Results will be disaggregated by age, sex and ethnicity, as well as other features to provide detailed information on the health of different population groups. In addition, a comparison will be made with the results from the 2006 New Zealand Mental Health Survey to provide a picture of the health of prisoners against that of the general population.

Part two of this article, which will cover the results of the study, will be reported in the next edition of the Practice Journal.


Understanding the current extent of mental health and drug and alcohol problems amongst New Zealand prisoners is a critical first step in Corrections being able to support them with appropriate treatment and other services. This study has generated extensive information that will enable Corrections to design and deliver integrated and effective treatment to meet the needs of prisoners with particular health issues.