Mortality after release from incarceration in New Zealand by gender: A national record linkage study

Abstract

Background

People who enter and leave places of incarceration experience considerable health inequities and are at increased risk of premature death compared to the general population. Causes of premature death in this population vary markedly between countries and so country-specific information is needed. Additionally, there is a lack of large population-based studies which can disaggregate mortality risk based on person and incarceration factors. This study is the first examination of mortality in the period following release from incarceration in New Zealand.

Methods

We linked deidentified administrative data on incarceration and release between 1 January 1998 and 31 December 2016 with national mortality data for the same period to examine mortality after release in those who had been incarcerated for at least 1 day. Age standardised mortality rates and mortality ratios compared to the general New Zealand population were calculated separately for men and women, for releases from remand compared with prison, and by cause of death and time since release.

Results

90,195 individuals (13% women, 49% Māori) were followed up for 9.4 years after release from incarceration, with 4,764 deaths over the follow-up period. The overall standardised mortality ratio was 3.3 (95% CI 3.2, 3.4) compared to the general population, and higher for women (3.8) than men (2.7). The most common causes of death were cardiovascular disease, cancer and suicide. Rates of death were similar following release from remand versus prison, however suicide rates were highest following release from remand. Regardless of the type of incarceration, mortality was highest in the first month after release.

Conclusion

Experience of incarceration in New Zealand is associated with high rates of mortality from both chronic conditions and external causes. There are urgent policy imperatives to recognise and actively address the increased health and mortality risks faced by people released from New Zealand prisons.

Highlights

• •People released from incarceration in NZ have more than three times the death rate of the general population.
• •The relative impact of incarceration on mortality was greater for women than men.
• •Chronic conditions are important causes of death after release from incarceration in NZ.
• •The mortality risk from all causes is highest in the first month after release.
• •Suicide rates were highest among those released from remand.

1. Introduction

Mass incarceration is increasingly being understood as a driver of health and social inequities (Massoglia & Pridemore, 2015; Massoglia & Remster, 2019; Wildeman, 2016; Wildeman & Wang, 2017). Prison populations have risen sharply in recent decades, with over 30 million adults released from prisons and other places of incarceration globally on an annual basis (Borschmann et al., 2020). Compared to the rest of the population, those who enter and leave places of incarceration experience considerable inequities and are at significantly increased risk of premature death (Borschmann et al., 2020; Fox et al., 2019). Similar to other colonial societies, the nation-state currently known as New Zealand (NZ) has extremely high rates of incarceration, particularly among the Indigenous Māori population (Department of Corrections, 2022; King et al., 2020). The rate of incarceration in NZ has been reported as 164 per 100,000 total population. This compares with Australia (167), Sweden (73), Denmark (72) and Finland (50). The United States has the highest rate of incarceration in the world at 629 per 100,000 total population (Fair & Walmsley, 2021).

As at March 2022, there are 7,669 people incarcerated in NZ prisons (2,988 people remanded in custody awaiting a trial or sentencing, and 4,593 people who have received a prison sentence) (Department of Corrections, 2022) out of an estimated total resident population of 5,127,100 (Stats NZ, 2022). Although the total number of people in NZ prisons has decreased since 2018, the proportion of people remanded in custody (currently 39% of the prison population) (Department of Corrections, 2022) has continued to grow over the last decade (Department of Corrections, 2021). Māori comprise 16.5% of the NZ population (Stats NZ, 2018) yet more than half of the people within NZ prisons are Māori (53.4%) (Department of Corrections, 2022). Thus, the rate of incarceration for Māori is 528 per 100,000 Māori population, a figure nearing reported incarceration rates for the United States.

Approximately 15,000 people are released from NZ prisons every year and of those released, 24% are re-incarcerated and 38.8% re-sentenced within 12-months of release (Department of Corrections, 2016). Of those initially sentenced to less than a year, 63.4% have been reported to be re-incarcerated within 12-months (Department of Corrections, 2021). As a result, there is likely to be rapid cycling of people entering and leaving prisons across the country.

International studies have reported that the risk of premature mortality for people released from prisons is significantly higher compared to the general population. A systematic review and meta-analysis including 18 cohorts (from three countries) examining all-cause mortality following release reported male all-cause standardised mortality ratios (SMR) ranging from 1.0 to 9.4, and female all-cause SMRs ranging from 2.6 to 41.4 (compared with the general population) (Zlodre & Fazel, 2012). Large cohort studies in the United States, Australia, Canada, Sweden, Iceland, and elsewhere have found increased risk of mortality following release from prisons both in the shorter term (weeks) (Borshmann et al., 2020; Bukten et al., 2017; Degenhardt et al., 2014; Lim et al., 2012; Merrall et al., 2010; Ødegård et al., 2010) and longer term (over a year) (Kinner et al., 2013). Studies show that mortality has a dose-response relationship with both length of time in prison (Patterson, 2013) and repeated short-term incarceration (Graham et al., 2015).

Suicide, drug overdose, and other external causes are responsible for many of the early deaths (Merrall et al., 2010; Jones & Maynard, 2013). Longer-term mortality has been related to infectious diseases (such as HIV and Hepatitis C), cardiovascular disease, respiratory disease, liver disease and specific cancers (such as liver and lung cancers) (Kinner et al., 2013; Massoglia & Pridemore, 2015; Massoglia & Remster, 2019). Although studies have consistently found an increased risk of mortality for people released from prisons compared to the general population, causes of death have tended to vary considerably between countries (Borshmann et al., 2020).

Internationally, there remain evidence gaps around mortality following release from prisons. These include inadequate sample size to disaggregate data by important factors including sociodemographic (age, ethnicity, socioeconomic factors), health (behaviours, health conditions, experiences of services, cause of death) and incarceration factors (time since release, whether a person is pre-trial or remand or sentenced, length of incarceration, previous incarceration) (Borshmann et al., 2020). Much of the evidence on mortality following release from incarceration is limited in its capacity to inform evidence-based responses to improve health, and reduce preventable mortality for people released from prisons. There is therefore a need for high-quality whole of population studies measuring a range of health outcomes (including mortality) to contribute to understanding of the impacts of incarceration, and the targeting of interventions to improve health and reduce premature mortality (Borshmann et al., 2020; Kinner & Young, 2018; Zlodre & Fazel, 2012). This work has also indicated a need for the development of appropriate methodological approaches to monitoring mortality post-release from places of incarceration (Borshmann et al., 2020; Kinner et al., 2013; Kinner & Forsyth, 2016).

With regard to the health of people incarcerated in NZ prisons, the Corrections Act, 2004 states that a person in prison is “entitled to receive medical treatment that is reasonably necessary” (Corrections Act, 2004, s75-1) and that the standard of healthcare available to people in prison “must be reasonably equivalent to the standard of healthcare available to the public” (Corrections Act, 2004, s75-2). Corrections provides primary healthcare services to people in prison (including primary dental and mental healthcare), basic emergency care, pharmaceuticals, and some disability support services. Other health and disability services are provided as part of the national system that funds public health and hospital level services for people in prisons (public health and preventive services, secondary and tertiary healthcare services as well as specialist mental health, alcohol and drug services, maternity and Well Child Tamariki Ora services, and disability support services). Five hospitals provide regional services for people with mental illness and learning/intellectual disability within the context of the justice system, including forensic hospital inpatient services, court liaison teams, community forensic services, assessments and transfer of mentally unwell individuals in prison to secure hospital facilities, and in-reach specialist (King, 2019). Consequently, coordination between the justice, corrections, and health sectors in the delivery of health and disability services before, during, and following release from prisons poses considerable challenges (National Advisory Committee on Health & Disability, 2010).

Conditions in NZ prisons, including their impact on the health of people in prison, have been the focus of numerous reports and commentaries over the last decade (Auditor General, 2008; Carr, 2007; National Advisory Committee on Health & Disability, 2010, Roguski & Chauvel, 2009; United Nations Committee against Torture, 2015), giving voice to the daily inhumaneness of the prison environment. For instance, use of solitary confinement and mechanical restraints such as ‘tie-down’ beds, and handcuffs on people in prison who are pregnant including whilst in labour and post-delivery of their babies (Carr & King, 2019; Lamusse, 2018; Office of the Children’s Commissioner, 2021; Shalev, 2017, 2020, 2021). Research into the impacts of incarceration on health outcomes in NZ however is still limited (King, 2019; National Advisory Committee on Health & Disability, 2010). To date, there have been two mental health surveys conducted in prisons in 1999 and 2015, showing high rates of mental health and addictions (Indig et al., 2016). Less is known about the physical health of people with the latest available data being from a 2005 national level survey conducted in NZ prisons (Ministry of Health, 2006). Corrections reports deaths in custody in its annual report. In 2020/21, there were 24 deaths in custody including 11 ‘unnatural deaths’ relating to ‘apparent suicides (Department of Corrections, 2021). To date, there have been no studies reporting on mortality following release from incarceration in NZ prisons.

Thus, our study focuses on what happens after release from incarceration in NZ prisons for three reasons. Firstly, this has been identified as a time of particularly high risk of adverse events (Borshmann et al., 2020; Kinner et al., 2013; Kinner & Wang, 2014; Massoglia & Pridemore, 2015). Secondly, community re-entry (release from incarceration and the days, weeks, months, years following) is a critical intervention point to address the health impacts of incarceration (Kinner & Wang, 2014; Mears & Cochran, 2014), and thirdly, as mass incarceration inevitably leads to issues of ‘mass re-entry’ of people from prisons into communities (Mears & Cochran, 2014), it is imperative to monitor the impacts of government carceral and other policies on the health of people incarcerated by the state.

The aims of this study were to: 1) describe mortality rates and main causes of death for adults released from incarceration in NZ prisons between the years 1998 and 2016; 2) compare mortality rates to the general population, adjusting for age differences; and, 3) investigate the impact of type of incarceration (prison vs remand) and time since release on mortality rates and causes of death.

2. Methods

2.1. Ethics and data use

Ethics was granted by University of Otago Human Research Ethics Committee (reference number: HD19/082). Data access was approved by Stats NZ. The results are not official statistics. They have been created for research purposes from the Integrated Data Infrastructure (IDI) which is managed by Stats NZ (Stats NZ, 2020).

2.2. Data source

The analyses were performed using Stats NZ’s Integrated Data Infrastructure (IDI), a large database containing person-level data for individuals who have interacted with NZ government services (Stats NZ, 2020). To create the IDI, births, tax and visa data are used to generate a list of people who have resided in NZ at any time since 1998 . This list forms a “spine” to which other datasets are probabilistically linked. Datasets include administrative data, data from non-governmental organisations, and some government survey data. A deidentified version of the IDI is available for researchers to analyse in a secure and safe environment (Milne et al., 2019; Stats NZ, 2020). We used the December 2019 refresh of the IDI.

Information about prison release was taken from Department of Corrections’ sentencing and remand data. Deaths were identified from the Ministry of Health’s mortality dataset. Demographic information was taken from the personal details table (which collates demographic information from across the IDI) and from the Ministry of Health’s National Health Index demographics dataset. 2.2% of the prison release population could not be linked to the spine of the IDI and therefore could not be linked to mortality or other data. These people were excluded from the study as the outcome could not be identified for this group.

Ethnicity was available within the personal details table, in Corrections data at the time of incarceration, and at the time of death as part of the death record. After a thorough data quality analysis of each source, we used ethnicity from the personal details table. This takes ethnicity from several sources in the IDI – Census, Department of Internal Affairs (birth and death registrations), Ministry of Health, Ministry of Education, and others – ranks these sources on data quality and assigns the ethnicity from the best quality source. Total response ethnicity is presented, where each person is included in each ethnic group they identify with, resulting in people being included in multiple ethnic groups.

2.3. Prison release cohort

The cohort includes people, released from prison or remand in NZ between 1 January 1998 and 31 December 2016, and aged 18 years or older at release. We excluded people from the cohort who died during incarceration, as the focus was on death after release from incarceration. Mortality rate calculations are based on those aged between 20 and 64 years at release. We excluded people aged <20 years because of the low numbers of deaths and the lack of standard population data for 18–19 year olds, and people aged over 65 years because of the low numbers of older people in the cohort (reducing the precision of estimates).

2.4. Computation

Analyses were performed using SAS Enterprise Guide 7.1. We identified all incarcerations for the cohort within the ‘Major Management Periods’ table in the Corrections’ datasets. We then grouped all consecutive and overlapping records to form continuous incarceration episodes, each with a date of incarceration, and date of release, to reflect the persons experience of incarceration rather than administrative classification. An individual could have multiple incarceration (and therefore out-side of prison and at risk of mortality) periods during the study time frame. Person-time at risk was counted from the date of release to the date of reincarceration, date of death, or the end of the study period, whichever came first. Age was derived at the end of each calendar year of follow up, to ensure person-time was counted against the correct age group.

We identified death registrations for the cohort from 1 January 1998 to 31 December 2016 in the mortality data. The underlying cause of death, as reported on the death certificate, was grouped into external and non-external (medical) causes, and further classified into eight sub-groups (Supplementary Table 1) adapted from the proposed international standards for research in this setting (Borshmann et al., 2020). Demographic data, including month of birth, gender and ethnicity, was derived from the personal details table. We used the date of death from the population cohort demographics data, as full date of death was required to ensure that we only counted deaths in the community after release. This included 18 deaths on the date of release: it was not possible to confirm whether these deaths occurred within incarceration facilities, or in the community.

2.5. Exposure

Any incarceration for greater than one day was the exposure. Releases were categorised as either 1) releases following remand-only periods of incarceration, or 2) releases following periods of incarceration that included time in prison (with or without prior time spent on remand).

2.6. Outcome

Mortality after release was the main outcome. We categorised deaths by the cause of death (Supplementary Table 1). We also used a simplified categorisation of deaths due to suicide, non-suicide external causes and medical (non-external) causes. Deaths were further categorised by time since release, into those which occurred less than a month of release, and those which occurred a month or longer after release.

2.7. Analyses

We calculated descriptive statistics about population released from incarceration, characteristics of the episode of incarceration (releases), and death after incarceration. Where possible, all results were stratified by gender, although some stratified results have not been included due to low numbers of events. Results were also stratified by type of incarceration (remand versus prison) and time since release, to explore the impact of these factors on death rates and causes. Further results stratified by ethnicity will be included in a subsequent paper.

In addition, we calculated age-standardised rates (ASR) and SMRs for deaths. The ASRs were deaths per 100,000 person-years, standardised to the WHO world standard population (Ahmad et al., 2001). The SMRs were the ratio of the death rate within the incarcerated population, compared to the death rate within the age and gender specific groups in the NZ general population. For both ASRs, and SMRs, we calculated all-cause and cause-specific iterations. Where numbers of outcomes were too small to calculate reliable ASRs, only SMRs were presented. This was the case when comparing mortality rates by time after release and type of incarceration. The denominators for the general population mortality rates were annual resident NZ population estimates from 1998 to 2016.

3. Results

3.1. Cohort description

A total of 93,762 individuals were identified from the Corrections dataset as having been released from remand or prison between 1 January 1998 and 31 December 2016. After exclusions, 90,195 individuals aged 18 years and over were included in the prison release cohort, 78,846 men and 11,349 women. Fig. 1 shows the exclusion process. These 90,195 individuals had 250,752 releases over the study period, a mean of 2.8 releases per person. The mean follow-up time per person over the study period was 9.4 years, and ranged from 1 day to 19 years.

Fig. 1.

Inclusion/exclusion flow diagram.

Table 1 provides information on the age and ethnicity of men and women released from prison or remand over the study period. The mean age at release was 31 years for both men and women, and 47% of men and 58% of women in the cohort were identified as Māori.

Table 1.

Demographics of people released from prison or remand in New Zealand, 1998 to 2016.

Demographics					Gender
		Total		Male		Female
Total	people	90,195		78,846		11,349
	releases	250,752		226,851		23,901
Age at release (years)	Mean	30.9		30.9		31.0
	IQ range	14		14		15
	Std dev	10.3		10.3		9.9
Age at release (number of releases)	18–24 years	84,819	34%	77,145	34%	7,674	32%
	25–34 years	85,671	34%	77,307	34%	8,364	35%
	35–44 years	52,467	21%	47,214	21%	5,253	22%
	45–54 years	21,090	8%	18,975	8%	2,115	9%
	55+ years	6,711	3%	6,213	3%	498	2%
Total response ethnicity	Māori	43,749	49%	37,209	47%	6,546	58%
	Pacific	11,307	13%	10,230	13%	1,074	9%
	Asian	3,594	4%	3,234	4%	360	3%
	MELAA	1,527	2%	1,410	2%	117	1%
	NZ European /Other	45,855	51%	40,170	51%	5,682	50%

Note: all counts are random rounded (base 3) due to confidentiality requirements so will not sum exactly to totals.

Table 2 provides information on incarceration characteristics for the study cohort. For both men and women nearly half of releases were from remand. The age distribution of releases was similar between men and women. Men had a mean of 2.9 releases while women had a mean of 2.1 releases over the study period. Three quarters of men in the cohort had been released from prison (as distinct from remand) at least once over the study period (one quarter only had a release from remand), while 69% of women had at least one release from prison. The total number of releases per year increased dramatically over the study period (1998–2016) with the increase primarily occurring in the years 1998–2007. Among men, the annual number of releases increased by 70%, while for women, there was an increase of 170%.

Table 2.

Characteristics of incarceration and release in New Zealand by gender, 1998 to 2016.

Characteristics			Gender
			Total	Males	Females
Total		Releases	250,755	226,852	23,903
		People	90,195	78,846	11,349
Releases per person		Mean	2.8	2.9	2.1
		IQ range	2	2	1
		Std dev	3.1	3.2	2.2
Incarceration type	Remand	Releases	118,311	106,596	11,715
		Peoplea	23,418	19,935	3,483
	Prison	Releases	132,444	120,255	12,189
		Peopleb	66,780	58,911	7,869
Year of release (no. of releases)		1998	8,709	8,067	642
		1999	10,653	9,921	732
		2000	10,662	9,852	810
		2001	11,763	10,890	873
		2002	11,478	10,620	858
		2003	12,042	11,043	999
		2004	13,041	11,694	1,347
		2005	13,278	12,018	1,260
		2006	14,352	12,981	1,371
		2007	15,183	13,719	1,464
		2008	13,926	12,522	1,404
		2009	15,486	13,947	1,539
		2010	15,111	13,479	1,632
		2011	14,736	13,209	1,527
		2012	14,121	12,624	1,497
		2013	13,125	11,820	1,305
		2014	13,095	11,745	1,350
		2015	14,214	12,681	1,533
		2016	15,774	14,016	1,758
Follow-up time after releasec (years)		Total person years	845,165	745,350	99,815
		Mean	9.4	9.5	8.8
		IQ range	9.0	9.1	8.4
		Std dev	5.4	5.4	5.2

Note: all counts are random rounded (base 3) due to confidentiality requirements so will not sum exactly to totals.

^aThis is a count of people incarcerated in remand only.

^bThis is a count of people that spent any time in prison during the study period (regardless of whether they spent time in remand).

^cFollow-up ended at the end of the study period, or when the person died or was reincarcerated.

3.2. Mortality after release

A total of 4,764 deaths occurred over the follow up period (Table 3), with most (91%) of these observed deaths among men (as the larger group in the study population). The numbers of deaths increased steadily with age for men, but for women the greatest number of deaths were seen in the 35–44 year age group. The majority of deaths occurred more than six months after release, although nearly 200 deaths occurred in the first two weeks after release.

Table 3.

Deaths after release from prison or remand by gender, 1998 to 2016.

Total		Gender
		Total	Males	Females
		4,764	4,326	438
Age at death	18–19	24	S	S
	20–24	285	261	24
	25–29	342	312	30
	30–34	381	339	42
	35–39	483	423	60
	40–44	582	498	84
	45–49	543	495	48
	50–54	585	522	63
	55–59	486	450	36
	60+	1,050	1,002	48
Duration from release to death (N)	1–14 days	195	186	9
	3–4 weeks	150	138	12
	1–6 months	426	399	27
	6–12 months	408	375	33
	>1 year	3,582	3,228	354
Duration from release to death (years)	Mean	5.0	5.0	5.4
	IQ range	6.9	6.9	6.3
	Std dev	4.6	4.6	4.6

S = suppressed value due to cell count <6.

Table 4 shows the breakdown of deaths after release from incarceration by primary cause of death (recorded on the death certificate). Overall the ASR of death for the prison release cohort aged 20–64 was 588 per 100,000 person-years, and higher for men (ASR 600.3) than for women (ASR 488). The most common causes of death for men were cardiovascular with an ASR of 129.4 per 100,000 person-years, followed by cancer (ASR 123.3), suicide (ASR 89.8) and transport-related (ASR 56). The most common causes for women were cancer (ASR 126.6), cardiovascular (ASR 88.6), suicide (ASR 65.7) and AOD poisoning (ASR 46.5).

Table 4.

Deaths after release by gender and cause of death, 1998 to 2016, compared to the general population.

	Total					Male					Female
	N	ASR*	95% CI	SMR**	95% CI	N	ASR	95% CI	SMR	95% CI	N	ASR	95% CI	SMR	95% CI
Total	4,008	588.0	567.9–608.0	3.3	3.2–3.4	3,597	600.3	578.8–621.7	2.7	2.6–2.8	411	488.0	433.2–542.7	3.8	3.4–4.1
AOD poisoning	321	38.9	34.4–43.5	12.5	11.2–13.9	273	37.9	33.1–42.6	8.7	7.7–9.8	48	46.5	31.9–61.0	25.5	18.7–33.9
Interpersonal violence	165	19.3	16.2–22.3	11.5	9.8–13.4	147	19.5	16.2–22.8	8.6	7.2–10.1	18	17.3	9.2–25.5	19.8	11.9–30.9
Other injuries	252	33.8	29.3–38.4	4.9	4.4–5.6	237	36.4	31.4–41.4	3.3	2.9–3.7	12	14.1	5.8–22.4	8.9	4.7–15.3
Suicide	741	86.9	80.3–93.4	5.5	5.1–5.9	675	89.8	82.8–96.9	3.6	3.4–3.9	66	65.7	48.4–82.9	9.1	7.0–11.6
Transport related	441	52.9	47.8–58.1	4.5	4.1–5.0	408	56.0	50.3–61.7	3.0	2.8–3.4	30	29.9	19.1–40.8	6.2	4.2–8.8
Cancer and other neoplasms	684	124.3	114.1–134.4	1.6	1.4–1.7	585	123.3	112.5–134.1	1.6	1.5–1.7	96	126.6	97.1–156.0	1.8	1.5–2.2
Cardiovascular diseases	753	125.1	115.2–134.9	3.0	2.8–3.3	684	129.4	118.8–140.1	2.2	2.0–2.3	69	88.6	64.0–113.2	4.4	3.4–5.6
Other	660	106.9	97.9–115.8	3.0	2.8–3.3	588	108.0	98.4–117.5	2.6	2.4–2.9	72	99.3	71.8–126.9	3.3	2.6–4.2

Note: all counts are random rounded (base 3) due to confidentiality requirements so will not sum exactly to totals.

* per 100,000 person years of follow up after release.

** age and gender standardised mortality ratio.

Overall, the standardised mortality ratio (SMR) was 3.3 (CI 3.2, 3.4) for the prison release population compared to the general NZ population, and higher for women (SMR 3.8) than men (SMR 2.7). The SMRs were highest from AOD poisoning and interpersonal violence for both men and women. For men the death rate from AOD poisoning was 8.7 times higher (CI 7.7, 9.8), and the death rate from interpersonal violence was 8.6 times higher than the general population (CI 7.2, 10.1). For women, the death rate from AOD poisoning was 25.5 times higher and the death rate from interpersonal violence was 19.8 times higher than the general population.

Table 5 compares mortality rates between those who had been released from prison and those who had been released directly from remand. The rates of death following release from remand are similar to the rates of death following release from prison, with the exception of suicide rates which are substantially higher following release from remand (ASR 125.6) than following release from prison (ASR 76.7).

Table 5.

Deaths after release by type of incarceration and cause, 1998 to 2016, compared to the general population.

Cause of Death	Prison					Remand only
	N	ASR*	95% CI	SMR**	95% CI	N	ASR	95% CI	SMR	95% CI
AOD poisoning	255	38.2	33.3–43.2	8.8	7.7–10.1	66	41.7	30.2–53.1	12.3	9.5–15.7
Interpersonal violence	135	19.7	16.2–23.2	9.2	7.6–11.0	30	17.6	11.1–24.1	10.2	7.0–14.5
Other injuries	S	33.9	28.8–39.0	3.3	2.8–3.8	S	32.3	22.9–41.8	5.0	3.8–6.6
Suicide	522	76.7	69.8–83.5	3.3	3.0–3.6	216	125.6	107.5–143.7	7.6	6.6–8.7
Transport related	354	54.3	48.4–60.3	3.1	2.8–3.5	87	47.6	37.0–58.2	4.2	3.4–5.2
Cancer and other neoplasms	549	123.1	111.9–134.3	1.6	1.4–1.7	132	128.9	104.1–153.6	1.6	1.3–1.9
Cardiovascular diseases	612	125.7	114.8–136.6	2.1	2.0–2.3	141	122.3	99.5–145.1	3.0	2.5–3.6
Other	525	107.2	97.2–117.3	2.6	2.4–2.8	138	102.2	82.7–121.7	3.2	2.7–3.8

S = supressed due to cell count <6.

Note: all counts are random rounded (base 3) due to confidentiality requirements so will not sum exactly to totals.

* per 100,000 person years of follow up after release.

** age and gender standardised mortality ratio.

Table 6 shows mortality by time after release, dichotomised to: 1) within a month of release; and, 2) beyond a month of release, and comparing those who have been released from remand with those who have been released from prison. Regardless of type of incarceration, mortality relative to the general population death rates were highest in the first month after release for all causes, with SMRs ranging from 9.9 for medical causes (95% CI 8.2, 11.8) up to 28.8 for suicide (95% CI 23.3, 35.4). However, in the first month following release from remand, compared with the general population, the SMR for suicide was markedly higher than among those released from prison (SMR 68.1 versus SMR 22.9). Beyond the first month, there was much less difference in the SMRs following release from remand versus release from prison. However, compared with the general population, suicide rates after release from remand still remained higher (SMR 6.7 following release from remand versus SMR 4.5 following release from prison).

Table 6.

Deaths within a month of release and at least a month post-release, 1998 to 2016, by cause of death and type of incarceration, compared to the general population.

Incarceration type	Cause of death	N		SMR
		Time from release
		<1 month	≥1 month	<1 month	95% CI	≥1 month	95% CI
All	Medical/non-external	120	1974	9.9	8.2–11.8	2.2	2.1–2.3
	Suicide	90	648	28.8	23.3–35.4	4.9	4.6–5.3
	Other external	84	1092	19.8	15.8–24.4	5.9	5.6–6.3
Prison	Medical/non-external	105	1584	10.0	8.2–12.1	2.2	2.1–2.3
	Suicide	63	459	22.9	17.6–29.3	4.5	4.1–4.9
	Other external	72	867	19.9	15.6–24.9	6.0	5.6–6.4
Remand only	Medical/non-external	15	393	16.7	9.4–27.6	2.3	2.1–2.5
	Suicide	27	186	68.1	45.6–97.8	6.7	5.8–7.7
	Other external	9	222	22.0	11.0–39.4	5.7	5.0–6.5

Note: all counts are random rounded (base 3) due to confidentiality requirements so will not sum exactly to totals.

4. Discussion

This study examined mortality among 90,195 people (13% women) released from prison or remand between 1998 and 2016, followed up for an average of 9.4 years, with an average of 2.5 releases per person and 4,764 deaths during the follow-up period. The most common causes of death for both men and women were cardiovascular disease, cancer and suicide, with the main cause of death for men being cardiovascular disease, and for women, cancer. Compared to the general population, the SMRs of deaths from all major causes were higher in those recently released from incarceration, ranging from 1.6 times higher for deaths from cancer up to 12.5 times higher for deaths from AOD poisoning.

Findings of this study mirror those of international studies reporting the very high risks of mortality during the community re-entry period, particularly within the weeks immediately following release from places from incarceration, but also over the longer term (Borshmann et al., 2020; Fox et al., 2019). Internationally, high risks of fatal opioid overdose have been reported as the predominant driver of increased mortality rates for people in the immediate weeks following release from incarceration compared with the general population (Fox et al., 2019; Merrall et al., 2010). However, findings from our study differed in that deaths from suicide were the driver of increased mortality rates compared with the general population in the weeks following release from incarceration, with the biggest difference found (SMR 68.1) amongst those who had most recently been released from remand. The increased risk of suicide post release from prison has previously been reported (Jones & Maynard, 2013; Merrall et al., 2010). A recent systematic review and meta-analysis reports that remand status is significantly associated with increased risk of suicide (Zhong et al., 2021). Our findings regarding increased mortality and remand status are particularly concerning within the context of NZ, where the proportion of people on remand (39% of the prison population) continues to grow.

In alignment with international studies examining longer-term follow-up, we also found cardio-vascular disease and cancer to be the most common causes of mortality (Binswanger et al., 2013). These are also the leading causes of death for the general NZ population (Ministry of Health, 2021). Our findings also aligned with other international studies reporting higher risks of death from suicide for women compared to men following release from incarceration (Fox et al., 2019). However, although higher death rates were seen from AOD poisoning and interpersonal violence for both men and women compared to the general population, for women, AOD poisoning deaths were 25.5 times higher, and deaths from interpersonal violence were 19.8 times higher than the general population.

This study has a number of strengths. As a population-based study it includes complete national data for 18 years of incarceration releases. It is also the first, to our knowledge, nationally linked cohort study of its kind, and demonstrates the importance of the early period following release from incarceration, particularly for external causes of death for women, and by remand status. Linkage to the national mortality collection allows complete follow-up data, with the exception of those who could not be linked or who died outside NZ. The large national dataset allowed for separate examination of mortality among women who have been incarcerated, and examination of specific causes of death and by remand status and time since release.

Routine data has its limitations however. As noted, it was not possible to link all of those who had been incarcerated to the ‘spine’ (the linkage population) and so it was not possible for the study to include everyone who had been released. However, the low proportion who were excluded (2%) means a low risk of substantive selection bias. The data on gender in national collections does not necessarily align with self-identified gender. The small numbers of under 20-year-olds in the dataset precluded examination of mortality in this group. Further examination of the health of children and young people in youth justice residences and prison youth units is thus urgently warranted. It was also not possible to examine the impacts of further factors such as length of incarceration and single vs repeat incarceration, and we aim to do this in our further work on this cohort.

Our findings reiterate that, due to different contexts that include driving factors and causes of preventable deaths and thus the need for appropriate policy responses, localised and timely data is critical to addressing the adverse health outcomes of people who enter and leave places of incarceration (Kinner & Forsyth, 2016). As it is the first study of mortality following release from prisons in NZ, this study paves the way for further research on the health of a population group that experience considerable marginalisation.

Mortality patterns seen in the population who have been released from incarceration to some extent reflects patterns of deaths seen in the general Māori population. There is a comprehensive evidence base regarding the inequities in health and disability outcomes experienced by Māori as a result of colonisation, coloniality and racism (Ministry of Health, 2015; King, 2019; Reid et al., 2019). However, further analyses from our work (included in a separate paper currently in preparation examining mortality following release from prison by ethnicity and led by Indigenous Māori authors on the team) demonstrates that for both Māori and non-Māori, incarceration is associated with a significantly higher risk of subsequent mortality.

In NZ, Government commissioned reports have called for fundamental transformation of the justice system, with a priority of addressing mass incarceration of Māori (Hapaitia te Oranga Tangata Safe and Effective Justice Programme, 2019; Te Uepū Hapai i te Ora: Safe and Effective Justice Advisory Group, 2019). Internationally, urgency around addressing mass incarceration has intensified in response to the COVID-19 pandemic impacts on health outcomes for people in places of incarceration, the staff who work there, and surrounding communities (Rapisarda & Byrne, 2020a; 2020b; 2020c; 2020d; Byrne et al., 2020; Henry, 2020; Montoya-Barthelemy et al., 2020; Rapisarda et al., 2020a; 2020b). Hence there have been increased calls for addressing mass incarceration through rapid decarceration (Alohan & Calvo, 2020; Minkler et al., 2020; National Academies of Sciences, Engineering, & Medicine, 2020; UNODC, WHO, UNAIDS, & OHCHR, 2020) moving towards humane, just and fair substitutions to the carceral state (American Public Health Association, 2020).

Achieving this in NZ requires a whole-of-government commitment to an equitable public health approach that reduces the number of people in places of incarceration via curbing admissions to youth justice residences and prisons, and facilitating early release from them (King et al., 2020). This will require inter-departmental work particularly between justice, corrections and the new health entities established under the current NZ health reforms (Department of the Prime Minister and Cabinet, 2022). Additionally, effective implementation of the health reforms will require clear ‘handover’ of the responsibility for funding and provision of health and disability services within prisons to these new health entities, which, under the PaeOra Healthy Futures Act, 2022, must also evaluate the delivery and performance of the services that they fund or provide, inclusive of those within prisons (Pae Ora Act, 2022). Reforms are thus an opportunity to improve the health and disability care for people within and following release from NZ prisons.

5. Conclusion

The findings of our study demonstrate the criticality of decision-making around ensuring safe pathways to freedom in the release of people from NZ prisons, and are of relevance to decision-makers in policy settings, as well as to practitioners working in health and social service settings (for instance, primary care, emergency medicine, mental health and addictions, family violence prevention, suicide prevention). We must not only recognise but also actively address the increased health risks faced by people released from NZ prisons, via facilitated access to income support and safe accommodation, and through comprehensive health and social service planning involving access to high-quality culturally safe health and disability care within prisons, to guaranteeing timely continuity of care and ongoing support from health and social services within communities upon release.

Approval and data access

Ethical approval for the study was granted by University of Otago Human Research Ethics Committee (reference number: HD19/082). Data access was approved by Stats NZ.

Funding

This study was funded by a grant from the University of Otago.

Author statement

R Cunningham: Conceptualization; Funding acquisition; Investigation; Methodology; Project administration; Supervision; Writing - original draft.

P King: Conceptualization; Funding acquisition; Investigation; Methodology; Writing - original draft.

K Telfer: Data curation; Formal analysis; Methodology; Visualization; Writing - review & editing.

S Crengle: Conceptualization; Methodology; Writing - review & editing.

J Carr: Conceptualization; Methodology; Writing - review & editing.

J Stanley: Methodology; Project administration; Supervision; Writing - review & editing.

S Gibb: Conceptualization; Methodology; Resources; Supervision; Validation; Writing - review & editing.

B Robson: Conceptualization; Funding acquisition; Methodology; Writing - review & editing.

Declaration of competing interest

The authors have no competing interests to declare.

Appendix A. Supplementary data

The following is the Supplementary data to this article:

Data availability

The authors do not have permission to share data.