Suicides in female prisoners in England and Wales, 1978-2004

We calculated, in narrow age bands, suicide rates for femaleprisoners compared with the general population between 1978and 2004. The standardised mortality ratio (SMR) for suicidewas 20.7 (95% CI 16.7–25.7), with a higher excess inyounger women (<25 years, SMR=40 (95% CI 29–57); $>=$ 25years, SMR=20 (95% CI 15–26)). There was a trend overtime for SMRs to have increased, supporting the need for recentnational initiatives for suicide prevention in prisoners.

INTRODUCTION

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INTRODUCTION

There are over 4000 women imprisoned in England and Wales, andthe number has more than doubled in a decade;¹ women constitute5–6% of all prisoners, a proportion that has steadilyrisen since the 1960s. Studies have reported high rates ofmental disorder,² self-harm³ and suicide.⁴ However, comparisonof suicide rates with the female general population has notbeen quantified and suicide trends in women prisoners are notreliably known. As suicide rates have changed for women inthe general population, with a reduction in age-standardisedrates in women aged over 45,⁵ comparison is necessary by calendaryear and in narrow age-bands. Furthermore, as base rates ofsuicide are low, an extended period is necessary to study trends. Therefore, we studied suicide mortality among females in Englishand Welsh prisons between 1978 and 2004 in comparison withage-specific background rates for the general female population.

Method

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Method

Following receipt of approval from the Prison Health ResearchEthics Committee, we sought all death certificates of sentencedand remanded female inmates during 1978–1997 from theMedical Research Unit, Office for National Statistics and,for 1998 to 2004, numbers of suicide by age band from the SaferCustody Group, Prison Service, Ministry of Justice. Suicidecases were defined as females with post-mortem findings ofsuicide (ICD–9⁶ codes E950–959) or deaths from`injury undetermined' whether accidentally or purposefullyinflicted (ICD–9 codes E980–989), and, in those without a post-mortem (four cases), where the coroner recordedsuicide or an open verdict. The total number of females inprison each year was determined from Home Office data usingstandard methods, and the average annual population was calculated.⁴ Standardised mortality ratios (SMRs) were calculated accordingto standard Prison Service age banding: 14–16, 17–20,21–24, 25–29, 30–39, 40–49 and 50+years from 1978 to 1989, with the first two groups changedto 15–17 and 18–20 from 1990. General populationdeath rates for suicide were requested from the Office for National Statistics to correspond to these exact age bands for eachyear between 1978 and 2004, including the revised age bandingfrom 1990. Trends over time were calculated over 5-year periodsusing linear regression with log transformed SMR on time period.The model assumptions were explored using residual analysisand diagnostic plots. Information on all-cause mortality was available for the period 1978–1997, and an overall SMRwas estimated using methods previously described.⁷ We also calculated SMRs by two larger age-bands (<25 years and $>=$ 25years). Information on social class, estimated from last occupationrecorded on death certificates was available for only ten prisonsuicides and not analysed further. We included an additionalanalysis to take into account the expected number of suicidesbased on the high prevalence of opioid dependence.⁸ For thisanalysis, we assumed a lifetime prevalence of opioid dependenceof 43.5% (the prevalence of opioid injectors⁹ in the late1990s multiplied by 1.5 to infer opioid users, as per previous work⁸). As this assumes that the prevalence of opioid dependencehas been unchanged during 1978–2004, we estimated expectedsuicide in two alternative models that assumed lower prevalencesin the first 15 years of two-thirds (i.e. 29%) and a half (i.e.22%).

Results

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Results

Between 1978 and 2004, 83 suicides in female prisoners wererecorded (online Table DS1): 163 suicides per 100 000 prisoners.The SMR for suicide at all ages was 20.7 (95% CI 16.7–25.7).Age-specific SMRs were calculated. There were no suicides inprisoners under 18 years. In those aged 18–20 years,the SMR was 70 (95% CI 44–113); 37 (95% CI 23–58)in those 21–24 years; 27 (95% CI 17–43) in those25–29 years; 17 (95% CI 10–27) in those 30–39years; 22 (95% CI 12–38) in those 40–49; and 8(95% CI 2–33) in those aged over 50. When larger age-bandswere used, those <25 years had an SMR of 40 (95% CI 29–57) compared with those $>=$ 25 years, who had an SMR of 20 (95% CI15–26). There was a significant increase in SMRs overthis time period (regression coefficient (β)=0.37, t=9.41,d.f.=5, P>0.001; Fig. 1). This did not change when thelast time period (2003–2004) was excluded from the analysis (β=0.32, t=8.16, d.f.=4, P=0.004).

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Fig. 1 Trend over time for SMRs for suicide in female prisoners 1978–2004. SMR, standardised mortality ratio.

For the subanalysis of all-cause mortality from 1978 to 1997(including deaths from natural causes in addition to suicide),43 deaths in custody were analysed. All-cause SMR was 3.0 (95%CI 2.3–4.1) and suicides constituted 60.5% of the deaths.The SMR for natural causes of death (i.e. excluding suicide,homicide and accidents) was 1.6 (95% CI 1.0–2.6). Therewere insufficient numbers to calculate the cause-specific SMRs.

When opioid dependence was accounted for,⁸ the annual numberof expected suicides was 0.30 compared with 3.07 actual suicidesper year over 1978–2004 (equivalent to SMR=10.2). Ifa lower prevalence of opioid dependence in the first 15 yearswas assumed, the annual numbers of expected suicides were 0.26(if prevalence was 29% in the earlier years) and 0.23 (if prevalencewas 22% in the earlier years, equivalent to SMR=13.3).

Discussion

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Discussion

For the past 25 years, suicide has been about 20 times morecommon in female prisoners in England and Wales than in thegeneral female population of similar ages. This excess hasbeen increasing steadily over recent decades and is more thanthe fivefold increase in SMR for suicide found in male prisoners.¹⁰Female prisoners aged <25 years had higher SMRs than olderinmates. The highest SMR in male prisoners was for the youngestage group (15–17 years).¹⁰ Together, these findingssuggest that younger prisoners are a particularly high-risk group. The strengths of this study include its long durationand the careful comparison with general population suiciderates by narrow age-bands and by calendar year.

The higher overall SMR for female prisoners compared with maleprisoners highlights a gender gap in suicide that has alsobeen found in recently discharged prisoners¹¹ but is lesspronounced in psychiatric patients. In psychiatric patients,the male to female ratio of suicides is 2:1 compared with 3:1in the general population.¹² The gender gap does not appearto be present in the SMR for all-cause mortality: in male prisoners,over the same time period, all-cause mortality SMR was 2.9,⁷compared with 3.0 reported here. One possible explanation forhigher SMR for suicide in female prisoners is that femalesentering prison may have higher prevalences of risk factorsassociated with suicide, such as depression,² previous self-harmand history of physical and sexual abuse. Substance misuse isa risk factor for prison suicides,¹³ and a systematic reviewhas shown that the relative excess of substance misuse in prisonerscompared with the general population is higher for female inmates.¹⁴Another explanation is that prison may specifically increasethe vulnerability of females to suicide. The impact of custodyon women with dependent children, to take one example, maybe relevant.¹⁵

Although social class information was limited, such differencesare unlikely to explain the SMR for suicide reported social classes.¹⁶ Some of the suicide excesses seen among prisonersmay relate to characteristics before imprisonment, such aspsychiatric illness and substance misuse.^2,14 The increasedmortality of opioid users, reported to be ten times the general population,¹⁷ accounted for about half the SMR. The reasonsfor the increasing SMR for prison suicide are likely to becomplex. One possible explanation is that the above-averageincrease in the number of women convicted of drug-related offences¹⁸may have led to increasing numbers of females entering prisonwith substance use problems. Our findings underscore the currentnational strategy to reduce risk in key high-risk groups suchas prisoners and to reduce the availability and lethality of methods.¹⁹ Further work, including investigations of near-lethalsuicide attempts²⁰ and case–control studies of prisoners,¹³is necessary to clarify the contribution of prison-relatedvariables such as overcrowding, distance from the prisoner'shome, length of time served and the proportion of pre-sentencedfemales, and provide information on other potentially modifiablerisk factors.

ACKNOWLEDGMENTS

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ACKNOWLEDGMENTS

This study was funded by Oxfordshire Health Services ResearchCommittee. We are grateful to Michael Keene from the SaferCustody Group for assistance with the data, Professor KeithHawton and Dr Lisa Marzano for helpful discussions, ProfessorJohn Danesh for methodological advice and Louise Linsell for statistical assistance.

REFERENCES

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