Centre for Suicide Research,University Department of Psychiatry, Warneford Hospital, Oxford
Centre for Statistics in Medicine, Institute of Health Sciences, Oxford, UK
Correspondence: Professor Keith Hawton, Centre for Suicide Research, University Department of Psychiatry, Warneford Hospital, Oxford OX3 7JX, UK. E-mail: keith.hawton{at}psych.ox.ac.uk
Declaration of interest None. Funding is detailed in Acknowledgements.
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ABSTRACT |
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Aims To investigate the risk of suicide after DSH during a long follow-up period.
Method A mortality follow-up study to 2000 was conducted on 11 583 patients who presented to hospital after DSH between 1978 and 1997.Data were obtained from a general hospital DSH register in Oxford and the Office for National Statistics, and from equivalent mortality registers in Scotland and Northern Ireland.
Results Three hundred patients had died by suicide or probable suicide.The risk in the first year of follow-up was 0.7% (95% CI 0.60.9%), which was 66 (95% CI 5282) times the annual risk of suicide in the general population.The risk after 5 years was 1.7%, at10 years 2.4% and at 15 years 3.0%.The risk was far higher in men than in women (hazard ratio 2.8,95% CI 2.23.6). In both genders it increased markedly with age at initial presentation.
Conclusions Following DSH there is a significant and persistent risk of suicide, which varies markedly between genders and age groups. Reduction in the risk of suicide following DSH must be a key element in national suicide prevention strategies.
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INTRODUCTION |
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Using a long-term monitoring system for deliberate self-harm, we have investigated the short-term and longer-term risk of suicide following this behaviour. We have also examined the risk according to gender and age subgroups, and over time.
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METHOD |
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Identification of suicides
Details of all individuals (name, gender and date of birth) who presented
during the study period were submitted to the Office for National Statistics
(ONS) for England and Wales. Tracing revealed whether these individuals were
alive or dead on 31 December 2000. It also provided information (including the
date) on those who had emigrated from England and Wales, moved to Ireland or
Scotland, or left the register for other reasons. Further tracing was done
through the Central Services Agency (Northern Ireland) and through the General
Register Office for Scotland. Copies of death certificates were obtained for
all those who had died. Deaths receiving a coroner's verdict of
suicide (ICD codes E950E959;
World Health Organization,
1992) were combined with those given a verdict of
undetermined cause (E980E989) or accidental
poisoning (E850E869) to create a probable suicide
group (henceforth referred to as suicides), because using
suicide verdicts alone underestimates overall mortality from suicide
(Charlton et al,
1992). Cases for which no information was available on whether the
person was alive or dead at any time during the follow-up period were excluded
from the study.
Estimation of risk of suicide
Risk of suicide was calculated in terms of the number of persons entering a
study period for whom outcome was known at the end of that period. Each
person's first presentation within the study period was used in the
calculation of risk over time. The risk of suicide within 1 year of deliberate
self-harm was compared with general population rates of suicide in England and
Wales. This comparison was restricted to suicides and deaths due to
undetermined cause. Numbers of suicides and general population statistics
categorised by gender and age groups for 1978, 1988 and 1998 were averaged and
then applied to the study sample to compute expected numbers of deaths. The
relative risk in the study sample was calculated as a ratio of actual
v. expected numbers of deaths.
Statistical analyses
All patients traced by the ONS for any length of time from their first
presentation were entered into a survival analysis. KaplanMeier curves
were plotted and log rank tests used to test for differences in suicide risk
between genders, age groups (1024 years, 2534 years, 3554
years, 55 years and over) and 5-year index periods (19781982,
19831987, 19881992, 19931997). Risks of suicide at
different time periods were estimated from this analysis, including 95%
confidence intervals. Cox's regression models were fitted, assuming
proportional hazards, to estimate risk over time and according to gender and
age at index episode. KaplanMeier curves are shown in this paper
truncated at 15 years of follow-up time, as numbers in some subgroups had by
then fallen to less than 20% of the original sample
(Pocock et al, 2002).
Analyses were carried out using the Statistical Package for the Social
Sciences version 10.0 (SPSS,
2000) and STATA version 7.0
(StataCorp, 2001).
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RESULTS |
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The majority of people in the sample were women and in the younger age
groups (Table 1). Most
self-harm episodes involved self-poisoning. The untraced patients did not
differ significantly from the traced patients in terms of either gender or
age. Somewhat fewer of the untraced patients had self-poisoned (84.3%
v. 89.4%) and more had self-injured (11.7% v. 7.6%;
2=23.85, d.f.=2, P<50.001). For those who were
traced the follow-up time ranged from 1 day to 23 years, with a median of 10.8
years.
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Deaths
A total of 1187 (10.2%) persons had died by the end of 2000. Three hundred
(2.6%) had died by suicide according to our definition. A suicide verdict was
recorded for 177 (59.0% of these), an open verdict for 82 (27.3%) and an
accidental poisoning verdict for 41 (13.7%). The most frequent method of
suicide was self-poisoning, with little difference between the genders in the
distribution of this and other methods of suicide
(Table 2). The majority,
however, had used a method different from that used in the index episode of
self-harm, with hanging and gas (usually car exhaust) being the most
frequent.
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Effects of gender and age
The overall risk of suicide within a year of deliberate self-harm
(Table 3) was 0.7% (95% CI
0.6%0.9%). It was far higher in males (1.1%) than in females (0.5%).
The figures for suicides at 5 years and 10 years indicate continuing risk.
After 15 years, 3.0% had died by suicide, including 4.8% of men and 1.8% of
women. Survival analysis (Fig.
1) shows that the risk of suicide was markedly greater in males
than in females throughout the follow-up period (log rank
2=80.47, d.f.=1, P<0.0001). This remained
significant after adjusting for age (log rank
2=76.53,
P<0.0001). A Cox model showed that over the 15-year follow-up
period the hazard ratio for males relative to females was 2.8 (95% CI
2.23.6). Figure 1 also
shows that the risk of suicide in both genders was highest during the period
immediately following self-harm.
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In both genders there was a marked escalation in risk of suicide with
increasing age at the time of the initial self-harm episode
(Table 3). Survival analyses
(Figs 2,
3) show that the age
differential in risk persisted throughout the follow-up period and was
statistically significant for both men (log rank 2=26.53,
P<0.0001) and women (log rank
2=51.73,
P<0.0001). The increased risk with age was particularly marked in
women aged 55 years and over. There was no significant interaction between
gender and age (likelihood ratio test,
2=2.71,
P=0.1). Thus both male gender and increasing age appear to be
independent risk factors.
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Risk and time period
We compared the risk of suicide during the follow-up period for patients
who first presented during each of four 5-year periods (19781982,
19831987, 19881992, 19931997). There was little
difference in risk (log rank 2=1.08, P=0.78),
indicating no major change in risk during the 20-year study period.
Risk of suicide in first year following deliberate self-harm
The overall age-standardised risk of suicide in the first year after
self-harm was 66 (95% CI 5282) times the annual risk of suicide in the
general population of England and Wales during the study period (based on
averaging rates for 1978, 1988 and 1998). In males it was 64 (95% CI
4685) times the general population risk and in females it was 90 (95%
CI 62126) times the risk. The relative risk increased with age. In
those aged 1024 years at initial presentation the risk was 35 (95% CI
1679) times the population risk in males and 75 (95% CI 35157)
times the risk in females, whereas in those aged 55 years and over the
comparable figures were 131 (95% CI 68252) for men and 158 (95% CI
85294) for women.
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DISCUSSION |
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Methodological issues
Follow-up to death or to the end of the follow-up period was possible in
92.6% of cases submitted for tracing. The main reason for failure of follow-up
was incomplete or inaccurate information on the individual's name or date of
birth. We do not know the impact of this on the results. The untraced patients
did not differ markedly from those who were traced with regard to age and
gender. There was a significant but small difference between the two groups of
patients in the methods of self-harm. The large sample size and high
proportion of traced patients mean, however, that this would have had little
impact on the results.
The identification of suicides through inclusion of death from undetermined cause and accidental poisonings as well as official suicides is accepted practice in suicide research (Charlton et al, 1992). Few deaths will be misidentified by this procedure (Linsley et al, 2001). However, some suicides may be missed owing to their inclusion in other categories (e.g. lone driver road traffic accidents).
Risk of suicide compared with other studies
The risk of suicide in the first year following deliberate self-harm (0.7%)
was somewhat lower than the 1% reported in an earlier study from the UK
(Hawton & Fagg, 1988). One
reason is that in our study we used survival analysis; using an analysis
comparable to that of the earlier study, the risk would be 0.8%. Because of
the much larger size of our study, the revised figure might be more accurate.
Other possible explanations for the difference include changes in the
characteristics of the self-harm population and improvements in clinical
services.
The risk in the first year after self-harm was 66 times the annual risk of suicide in England and Wales, confirming the large degree of excess risk of suicide in these patients. Although risk of suicide is highest in the initial period following self-harm there is clearly a significant risk even many years later. The proportion of the sample dying from suicide following self-harm is lower than in many studies from other countries (Rygnestad, 1988; Suokas & Lönnqvist, 1991; Nordentoft et al, 1993; Sakinofsky, 2000), and this has been confirmed in a recent systematic review (Owens et al, 2002). This probably reflects differences in the self-harm populations such patients in the UK include more young people (Schmidtke et al, 1996), in whom we have shown that the risk is lower and also differences in general population suicide rates.
Age and gender
In keeping with the findings of most earlier studies
(Nordström et al,
1995; Sakinofsky,
2000; Suokas et al,
2001) the risk of suicide was far higher in men than in women
throughout the follow-up period. We have shown that the risk increases
markedly with age at the time of self-harm. The risk in those aged 55 years
and over was seven times greater than in those aged 1024 years in the
first year of follow-up, and nearly that after 5 years. This was reflected in
the risk relative to the general population rate in different age groups. This
underlines the need for clinicians to be especially vigilant for suicide risk
in older people presenting with deliberate self-harm.
Methods of suicide
The methods of suicide used by the people investigated in this study
differed somewhat from suicides in general in the UK in that in males
self-poisoning was more common. The fact that most of the latter had used
self-poisoning in their initial self-harm episodes indicates that persistence
with the original method is not uncommon. The majority of suicides, however,
involved a method different from that used in the original episode.
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Clinical Implications and Limitations |
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LIMITATIONS
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ACKNOWLEDGMENTS |
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Received for publication October 3, 2002. Revision received January 24, 2003. Accepted for publication February 5, 2003.
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