Centre for Suicide Research, University Department of Psychiatry, Warneford Hospital, 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 detailed in Acknowledgements.
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ABSTRACT |
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Aims To investigate the long-term risk of suicide associated with repetition of DSH by gender, age and frequency of repetition.
Method A mortality follow-up study to the year 2000 was conducted on 11 583 people who presented to the general hospital in Oxford between 1978 and 1997. Repetition of DSH was determined from reported episodes prior to the index episode and episodes presenting to the same hospital during the follow-up period. Deaths were identified through national registers.
Results Thirty-nine per cent of patients repeated the DSH. They were at greater relative risk of suicide than the single-episode DSH group (2.24; 95% CI 1.772.84). The relative risk of suicide in the repeated DSH group compared with the single-episode DSH group was greater in females (3.5; 95% CI 1.32.4) than males (1.8; 95% CI 2.35.3) and was inversely related to age (up to 54 years). Suicide risk increased further with multiple repeat episodes of DSH in females.
Conclusions Repetition of DSH is associated with an increased risk of suicide in males and females. Repetition may be a better indicator of risk in females, especially young females.
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INTRODUCTION |
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METHOD |
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Repetition and mortality
Patients were followed up until the end of December 2000; information
regarding repetition and mortality was available for a potential maximum of 23
years.
Information on whether a patient had had an episode of DSH prior to the index episode was obtained through clinical interview. This was combined with data on episodes leading to referral to the same hospital during the follow-up period to allow all available data on repetition for each patient to be used, including the number of episodes and the distribution of episodes over time. For the purposes of this study, the repeated DSH group comprised patients who reported an episode of DSH prior to their index episode or who had a repeat episode of DSH during the follow-up period (or both). The single-episode DSH group comprised those with only an index episode of DSH. Those patients for whom there was no information on DSH history prior to the index episode were assumed to have no previous episodes.
Mortality status was determined by tracing the individual names and dates of birth against a national registry held by the Office for National Statistics (ONS) for England and Wales. The equivalent registries in Scotland and Northern Ireland were consulted for those found to have left the ONS register. Causes of death were obtained from death certificates supplied by the ONS.
Suicide was defined in line with current research practice (Adelstein & Mardon, 1975; Charlton et al, 1992) based on coroners' verdicts of suicide (ICD code E950E959), undetermined cause (E980E989) or accidental poisoning (E850E869). Patients who died from causes other than suicide, or who were alive at the end of the follow-up period, were included in a non-suicide group.
Statistical analyses
All patients traced by the ONS for any length of time from their first
presentation were entered into survival analyses. KaplanMeier curves
were plotted and log-rank tests were used to test for differences in suicide
risk between genders and age groups by DSH repetition status. Cox's regression
models were fitted, testing for proportional hazards to estimate risk over
time and according to gender and age at index episode.
The KaplanMeier curves shown in this paper are truncated at 15 years of follow-up time because numbers in some sub-groups had fallen by then to <20% of the original sample (Pocock et al, 2002). Analyses were carried out using SPSS version 10.0 for Windows.
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RESULTS |
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At the time of the index episode, 2704 (23.3%) patients reported at least one previous episode (1043, 22.6% males; 1661, 23.9% females). During the follow-up period, 2666 patients (23.0%) repeated the DSH (1073, 23.2% males; 1593, 22.9% females). By combining information about episodes prior to the index episode with data on repetition during the follow-up period, 4540 (39.2%) were found to have repeated the DSH overall (1811, 39.2% males; 2729, 39.2% females). In total there were 18 582 DSH episodes in the study period.
Repetition and suicide risk
Survival analysis showed that those who reported an episode of DSH prior to
their index episode were at significantly greater risk of dying by suicide
than those whose index episode was their first (log rank test:
2=27.06, P<0.001). Using our definition of
repeated DSH (i.e. combining information on DSH repetition status at index
episode with information about episodes during the follow-up period) showed a
greater difference in risk between the repeated DSH group and the
single-episode DSH group (log rank test:
2=54.54,
P<0.001) (Fig.
1).
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Survival analyses, using all data on repetition for the two genders separately, confirmed that those in the repeated DSH group were at significantly greater risk than those in the single-episode DSH group for both males (hazard ratio 1.88, P<0.001, 95% CI 1.422.50) and females (hazard ratio 3.58, P<0.001, 95% CI 2.385.40) (Figs 2 and 3).
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The risk of suicide within 1 year of the index episode of DSH (Table 1) was 0.6% 95% CI 0.50.8) for the single-episode DSH group and 0.9% (95% CI interval 0.61.2) for the repeated DSH group. The difference in risk between the two groups increased with time: after 15 years 1.9% (95% CI 1.52.3) of the single-episode DSH group and 4.7% (95% CI 3.95.4) of the repeated DSH group had died by suicide (relative risk=2.24; 95% CI 1.772.84).
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Males in the repeated DSH group were at the greatest risk of suicide and females in the single-episode DSH group were at the least risk (Table 1). Within gender, the relative risk of suicide between the repeated DSH group and the single-episode DSH group over the study period was greater for females (3.5; 95% CI 2.35.3) than males (1.8; 95% CI 1.32.4). The absolute risk for males regardless of repetition status was, however, higher than that of females in the repeated DSH group.
A comparison of risk of suicide according to repetition status and age group (Table 2) showed that up to the age of 54 years the ratio of risk of suicide in the repeated DSH group compared with the single-episode DSH group was inversely related to age. Thus, the ratio was particularly high in the youngest age group (10- to 24-year-olds). In this age group the relative risk of the repeated DSH group compared with the single-episode DSH group in males was 2.0 (95% CI 1.23.3) and in females was 7.1 (95% CI 2.917.3). Thus, young females in the repeated DSH group were at particularly increased risk of dying by suicide compared with those in the single-episode DSH group. In fact, 25 (81%) out of 31 young females who died by suicide were in the repeated DSH group.
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Multiple repetition
All data on repetition were used to look at the comparative risk of suicide
between those with more than two episodes including the index episode
(multiple repetition) and two episodes only (single repetition). Thirty-four
per cent (1532) of the repeated DSH group had more than two episodes (see
Table 3). Overall, these
patients were at an increased risk of death by suicide than were those with
only two episodes of DSH over the follow-up period (log rank test:
2=4.65, P=0.031). Survival analysis by gender
revealed that females in the multiple repetition group were at an increased
risk of suicide compared with the single repetition group (log rank test:
2=5.98, P=0.015), but in males this was not so (log
rank test:
2=0.56, P=0.456).
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Survival time between last DSH episode and suicide
The time between the date of the last recorded DSH episode during the study
period and the date of suicide was compared for the repeated DSH group and the
single-episode DSH group (Table
4). Those in the repeated DSH group had a shorter delay between
the last DSH episode and suicide than did those in the single-episode DSH
group (log rank test: 2=47.55, P<0.001). Among the
whole study sample, females survived for a shorter time than males following
the last episode (log rank test:
2=19.45,
P<0.001). Of those who died by suicide, males in the repeated DSH
group survived for almost twice as long following their last episode as
females in the repeated DSH group. Among those in the single-episode DSH group
who died by suicide, males survived nearly three times as long as females.
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DISCUSSION |
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Methodological issues
The number of repeat DSH episodes recorded will be an underestimate of the
true number because only repeat episodes that resulted in presentation to the
same general hospital as the index episode could be recorded. Episodes that
presented to other hospitals and those that did not result in hospital
presentation would not have been identified unless they occurred prior to the
index episode.
Our method of identifying suicides by combining suicide verdicts with those of undetermined cause and accidental death due to poisoning was used because taking suicide verdicts alone underestimates the overall mortality from suicide (Charlton et al, 1992). The use of a national register to trace patients permitted an identification of outcome that was as accurate as possible because those who had changed names (especially females) and those who had moved away from Oxford during the follow-up period could still be traced. A drawback to the study is that it is based on patients presenting to only one general hospital. This hospital is, however, the main hospital for the catchment area. Also, the cohort size is very large compared with other studies. This permitted analyses by gender and age.
Repetition of DSH
The proportion of patients who had repeated the DSH at the time of the
index episode (23.3%) is well within the wide range that has been reported
elsewhere (Sakinofsky, 2000;
Owens et al, 2002). There was little difference in the proportions of males and females who had
repeated the DSH at index presentation. There was also little difference
between the proportions of males and females who repeated the DSH during the
follow-up period, which is consistent with the findings of other studies
(Morgan et al, 1976;
Bancroft & Marsack, 1977;
Owens et al, 2002), although none has had access to such large cohorts.
Repetition and suicide risk
The results confirm that repetition of DSH is associated with increased
risk of eventual suicide (Hawton &
Fagg, 1988; Tejedor et
al, 1999; Owens et
al, 2002). The increased risk for those in the repeated DSH
group in both the short and longer term compared with those in the
single-episode DSH group suggests that detailed enquiry about previous DSH
history is important in the assessment of risk. This should also include
asking about episodes that have not resulted in presentation to hospital.
Although repetition of DSH may be one of the strongest risk factors for death by suicide (overall, it was confirmed in 59.9% of the suicides), it is also important to note that suicide occurred in a small minority of cases overall: 4.7% of those in the repeated DSH group died by suicide compared with 1.9% of those in the single-episode DSH group over 15 years. Attention to other risk factors (Sakinofsky, 2000) is also clearly necessary, although the difficulty in predicting the risk of suicide should not be underestimated (Hawton, 1987; Goldney, 2000).
This is the first study known to us that has looked at the risk of suicide according to repetition of DSH over such a long time period (15 years). It appears that repetition of DSH, especially when account is taken of repeat epsidoes during follow-up, is associated with continuing suicide risk, whereas for those in the single-episode DSH group there is a levelling-off of risk. Of course, further repeat episodes are likely to indicate ongoing or recurrent psychiatric and psychosocial problems, which may explain why risk persists. Nevertheless, the recurrence of actual self-harm is clearly a poor prognostic sign with regard to possible future suicide.
Risk associated with repetition by gender, age and number of repeats
Although male DSH patients have a greater overall risk of suicide than
female patients (Hawton et al,
2003), the relative risk in the repeated DSH group compared with
the single-episode DSH group is greater in females. Very young females in the
repeated DSH group have a particularly high risk compared with those in the
single-episode DSH group at the same-age. Thus, information about repetition
may be more informative about future suicide risk in females than in males,
and may be particularly useful in young females.
Because this is the only study we are aware of that has examined the risk of suicide in relation to repetition of DSH by both gender and age group, there is little previous work with which to compare our findings. However, our findings are consistent with the direction of the findings reported by Bancroft & Marsack (1977).
Among all those in the repeated DSH group, those who engaged in multiple (more than two) episodes of DSH were at a significantly greater risk of suicide than those who repeated the DSH only once. The proportion of those with more than two episodes of DSH is consistent with that found elsewhere (Kreitman & Casey, 1988). However, the increased risk in the multiple repetition group of the present study was almost entirely accounted for by females, which suggests that multiple repetition of DSH is a better predictor of risk in females than it is in males.
A shorter time was found between the last episode of DSH and death for those in the repeated DSH group compared with those in the single-episode DSH group. This may simply represent the greater risk in the repeated DSH group. However, the gender difference in time between the last DSH and suicide in both the repeated DSH group and the single-episode DSH group may indicate a gender difference in the persistence of risk of suicide behaviour. This requires further investigation.
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Clinical Implications and Limitations |
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LIMITATIONS
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ACKNOWLEDGMENTS |
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REFERENCES |
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Received for publication August 18, 2003. Revision received January 12, 2004. Accepted for publication January 24, 2004.