Department of Social Medicine, University of Bristol, London
Social Survey Division, Office for National Statistics, London
WHO Collaborating Centre, Institute of Psychiatry, London, UK
Division of Psychiatry, University of Bristol, Bristol, UK
Correspondence: David Gunnell, Department of Social Medicine, University of Bristol, Canynge Hall, Whiteladies Road, Bristol BS8 2PR, UK. Tel: 0117 9287253; fax: 0117 9287204; e-mail: D.J.Gunnell{at}Bristol.ac.uk
Declaration of interest None. Funding detailed in Acknowledgements.
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ABSTRACT |
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Aims To determine the factors associated with the development of, and recovery from, suicidal thoughts.
Method An 18-month follow-up survey investigated 2404 of the adults who took part in the second National Psychiatric Morbidity Survey.
Results The annual incidence of suicidal thoughts was 2.3%. Incidence was highest in women and among 16- to 24-year-olds. Increased incidence was associated with not being in a stable relationship, low levels of social support and being unemployed. Fifty-seven per cent of those with suicidal thoughts at baseline had recovered by the 18-month follow-up interview.
Conclusions Risk factors for suicidal thoughts are similar to those for completed suicide, although the age and gender patterning is different. Fewer than 1 in 200 people who experience suicidal thoughts go on to complete suicide. Further study into explanations for the differences in the epidemiology of suicidal thoughts and suicide is crucial to understanding the pathways (protective and precipitating) linking suicidal thoughts to completed suicide and should help inform effective prevention of suicide.
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INTRODUCTION |
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METHOD |
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Definitions
Suicidal thoughts were defined as a positive response to the question,
Have you thought of taking your life, even if you would not really do
it? This question was drawn from one used in a study of suicidal
thoughts in the USA (Paykel et
al, 1974). Two other suicide-related questions about
life-weariness were asked in the National Survey of Psychiatric
Morbidity (Have you felt that life was not worth living? and
Have you wished that you were dead?), and other researchers
(Goldney et al, 2000;
Watson et al, 2001)
and a previous analysis of this data-set
(Gunnell & Harboard, 2003) have used positive responses to such questions in broader definitions of
suicidal thoughts (Goldney et al,
2000; Watson et al,
2001; Meltzer et al,
2002). This analysis, however, is based on the more restricted
definition.
In the baseline survey people were asked whether they had experienced suicidal thoughts in the past week, the past year or at some other point in their lives. At the 18-month follow-up they were also asked if they had experienced suicidal thoughts in the past week, the past year or since the last interview.
We undertook two separate analyses, first to assess factors associated with the new occurrence of suicidal thoughts in people without suicidal thoughts in the year before the baseline interview; and second, to assess factors associated with recovery in people with suicidal thoughts in the year before the baseline survey. We defined recovery as the absence of suicidal thoughts since the baseline interview, as reported at follow-up. We assessed the effect of the following factors on incidence and recovery:
We assessed the effects on recovery of the following additional factors: counselling, antidepressant therapy and contact with health care professionals; these variables were self-reported by the survey members. The mean interval between the two interviews was 535 days (interquartile range 519555).
Statistical methods
Analyses were carried out in Stata version 7.0
(Stata, 2001) using the
SVY family of commands designed specifically for data from sample
surveys to take account of the complex sample design. The sample weighting
adjusted the age, gender and geographic distribution of the sample to that of
the national population, and also accounted for selection probability for the
follow-up survey (all those with CISR scores above 5 at the initial
survey, but only 1 in 5 of those with CISR scores of 05) and a
correction for differential non-response. Percentage rates were obtained using
SVYTAB. To calculate the annual incidence of suicidal thoughts we
assumed constant incidence over the 18-month follow-up; as such an assumption
is improbable for recovery, we present 18-month recovery rates. Odds ratios
and confidence intervals were calculated using SVYLOGIT. Tests for
interaction were performed using SVYTEST to calculate adjusted Wald
tests.
Our initial models examined associations with each of the explanatory variables in men and women separately controlling for age (in 10-year age bands) and baseline CISR score (in four bands). To investigate gender differences in the patterns of association we fitted interaction terms between gender and the following variables:
We fitted a final multivariable model using data from men and women combined and including all the factors shown in the initial models to be associated (P<0.20) with the incidence of suicidal thoughts after controlling for age and CISR score.
We examined the influence of change in CISR score, newly occurring life events, change in income and employment status over the follow-up period on the incidence of suicidal thoughts. For all other variables too few people experienced a change in status over the follow-up period to enable investigation of these changes. As only around half of the respondents reported precise house-hold income at baseline and follow-up, but 96% reported individual income at both time points, our analysis of change in income is based on change in the individuals income.
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RESULTS |
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Table 1 presents the association of age and CISR with the development of suicidal thoughts. With the exception of those aged 1624 years, who had a risk 23 times greater than most other age groups, the incidence of suicidal thoughts varied little with age but was strongly associated with CISR score at baseline: compared with those scoring 05, those with scores of 18 and over had a risk that was 8 times greater in men and 28 times greater in women. There was weak evidence that the effect of age on risk differed in men and women (Pinteraction=0.063). The effect of CISR on risk also showed an apparent difference between the genders (Pinteraction=0.072), with a higher risk in women with CISR scores above 5 than in men.
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Associations adjusted for age and CISR of social and economic variables with the occurrence of suicidal thoughts are shown in Table 2. Married, cohabiting and widowed individuals were the least likely to develop suicidal thoughts. Divorced, separated and single individuals were approximately twice as likely as married individuals to develop suicidal thoughts, after adjusting for age and CISR score at the first interview. The development of suicidal thoughts was associated with having a small support group and experiencing more life events prior to the baseline interview. There was statistical evidence that the associations with life events were stronger in women than in men (Pinteraction=0.028), but this was not the case for the size of the primary support group (Pinteraction=0.16). Measures of low socio-economic position low income, low occupational social class, living in rented accommodation and unemployment were associated with increased risk. Although associations of some of the measures of socio-economic position were stronger in men than in women, there was no strong statistical evidence of effect modification. Values of P for interaction between gender and social class and between gender and unemployment were 0.36 and 0.18 respectively.
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In the multivariable model (Table 3), based on combined data from both genders, associations with marital status and size of the primary support group were little changed, and the association with life events was somewhat attenuated. In contrast, associations with the economic variables social class, income and housing tenure were greatly attenuated, although the association with unemployment was little changed. This attenuation was largely due to the fact that all four measures of economic position were correlated with one another, and was not due to controlling for the other social and life event measures.
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Incidence of suicidal thoughts in relation to change in risk factors
Compared with those whose CISR score changed by less than 6 points
over the 12-month follow-up, people whose score increased by 6 points or more
were at greatly increased risk of developing suicidal thoughts (OR=9.9, 95% CI
5.318.4) (Table 4).
Likewise, reduction in CISR score by 6 points or more was associated
with a reduced risk of developing suicidal thoughts (OR=0.3, 95% CI 0.1 to
0.6). Twenty-six people lost their job between the baseline and follow-up
interview compared with those who remained employed, these individuals
had an almost fourfold greater risk of developing suicidal thoughts. The 29
people who were unemployed at both assessments had a fourfold increased risk
of developing suicidal thoughts. Changes in the individuals income were
not associated with risk of developing suicidal thoughts.
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Factors associated with recovery from suicidal thoughts
A total of 164 participants reported having experienced suicidal thoughts
in the 12 months before the initial interview, of whom 84 reported no longer
experiencing them at the follow-up interview. After adjustments for the
sampling fraction, the age- and gender-standardised recovery rate at 18 months
was 56.8% (95% CI 46.566.5); men 53.3% (95% CI 38.167.9) and
women 59.9% (95% CI 46.971.7).
Patterns of recovery in relation to age, gender and baseline CISR score are shown in Table 5. Odds ratios greater than 1 indicate factors associated with recovery. Recovery was somewhat more likely in women and in those aged <25 and 6574 years, and was strongly associated with having a low CISR score at baseline. Social and economic factors associated with a lower likelihood of recovery were similar to those associated with the risk of occurrence although, because of the small sample size, the effect estimates have wide confidence intervals including 1.00 (Table 6). Those who were unemployed at the time of the initial interview had a markedly reduced likelihood of recovery (adjusted OR=0.24, 95% CI 0.041.49). The economically inactive (homemakers, retired people and students) also had less likelihood of recovery (adjusted OR=0.28, 95% CI 0.120.65). The power for detecting differences between the genders in relation to recovery was low, but an apparent difference was found between men and women in regard to employment status (Pinteraction=0.016): the likelihood of recovery for unemployed or economically inactive men (adjusted OR=0.08, 95% CI 0.020.29) relative to employed men was worse than for the same comparison in women (adjusted OR=0.40, 95% CI 0.121.31). Similarly, a gender difference was found in the effects of income on recovery (Pinteraction=0.003): low-income men were less likely to recover than low-income women.
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Recovery in relation to change in risk factor status
Improvements in CISR score were the strongest predictor of recovery
from suicidal thoughts. Compared with those whose CISR score changed by
only 5 units, those with an increase in CISR score of 6 or more had a
markedly reduced likelihood of recovery (OR=0.13, 95% CI 0.030.54). In
contrast, those whose score decreased by 6 or more points had a greater
likelihood of recovery (OR=2.86, 95% CI 1.177.00). Individuals who were
in employment at both interview points were most likely to recover, but few
suicidal individuals changed their employment status between the two
interviews. There was no evidence that change in an individuals income
was associated with recovery (Ptrend=0.66). There was weak
evidence that life events occurring since the baseline interview prevented
recovery (Ptrend=0.13).
Influence of health care on recovery
We examined whether people who reported taking antidepressant medication or
being under the care of their general practitioner, a counsellor or other
mental health professional were more likely to have recovered by the 18-month
follow-up interview than those not receiving such care at baseline
(Table 7). We found that those
in receipt of such treatment were less likely to recover, even after
controlling for disease severity at baseline as indexed by CISR score.
This finding of a lack of benefit from health care intervention was unaltered
when we restricted our analysis to those reporting suicidal thoughts in the
week before the baseline interview and used as a measure of recovery suicidal
thoughts in the week before the follow-up interview.
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DISCUSSION |
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The evidence that those receiving antidepressants, counselling or in contact with health care professionals were less likely to recover contrasts with the well-documented beneficial effects of some therapies (Freemantle et al, 1993). It is likely that the observed patterns reflect biases due to differences in disease severity in those receiving and not receiving treatment which were inadequately controlled for in models adjusting for CISR scores.
Strengths and limitations of the study
To the best of our knowledge, this is the largest prospective investigation
of the incidence of suicidal thoughts worldwide. The large study and sampling
procedure meant we had sufficient power to investigate factors associated both
with incidence and recovery. The detailed measures of psychiatric morbidity
meant we could investigate the effect of risk factors independent of the
degree of psychopathology. There are two main limitations. First, only
two-thirds of those sampled in the baseline and follow-up surveys were
interviewed. Such levels of non-response are typical of those found in studies
of this sort. Our weighting procedures took account of differential
non-response with respect to the measured characteristics of survey members;
however, our estimates of risk factor associations might be biased if their
relationship with the occurrence of suicidal thoughts differed in those who
were and were not interviewed. We anticipate that these effects would lead to
underestimation of incidence and overestimation of recovery, as those with
psychiatric disorder are less likely to respond to surveys of this sort. We
have no reason to believe that risk factor associations would differ between
those interviewed and the non-responders. The second main limitation is that
the measurement of suicidal thoughts depends upon self-report and recall over
an 18-month period. It is possible that there are gender and social class
biases in the reporting of psychological symptoms in interviews of this sort,
with men and people from lower social class backgrounds under-reporting
symptoms, thereby distorting patterns of association
(Stansfeld & Marmot, 1992;
Piccinelli & Wilkinson,
2000).
Our definition for suicidal thoughts (a positive response to the question Have you thought of taking your life, even if you would not really do it?) is somewhat weaker than that used in some analyses (Kessler et al, 1999; Hintikka et al, 2001). For example, Hintikka et al (2001) defined suicidal thoughts as positive responses to the questions I have definite plans to commit suicide and I would kill myself if I had the chance. Some people who responded yes to our question might have been at lower suicide risk than those responding positively to Hintikkas. Suicide risk is likely to be higher among some sub-groups of patients, for example those whose thoughts include the formulation of specific plans for suicide. We investigated the effects of using a wider definition of suicidal thoughts, including notions of life-weariness as used in other studies (Goldney et al, 2000; Watson et al, 2001). This resulted in an approximately 50% higher estimate of incidence. However, multivariable analysis of the data-set using this wider definition did not alter our main findings (results not shown).
Comparison with other studies
The only other prospective investigation of suicidal thoughts in a general
population sample of men and women that we are aware of is a questionnaire
follow-up of 1600 people in Finland
(Hintikka et al,
2001). The Finnish study reported risks of similar magnitude to
those seen in our study for levels of mental illness, unemployment and alcohol
misuse. In keeping with our finding, associations with unemployment were
strongest in men (Hintikka et al,
2001). In contrast to our finding, the Finnish study reported a
higher incidence of suicidal thoughts in men than in women; this is at odds
with most other studies of this issue
(Weissman et al,
1999). It is note-worthy that Helsinki was the only centre in the
World Health Organization multicentre study of self-harm where there were more
episodes in men than in women (Michel
et al, 2000). Our finding of a high incidence of suicidal
thoughts in those aged 1624 years supports those of previous UK studies
(Paykel et al, 1974;
Thomas et al, 2002)
as well as other national cross-sectional research
(Kessler et al, 1999;
Kuo et al, 2001;
Renberg, 2001), although age
associations differ in Iceland
(Vilhjalmsson et al,
1998).
How closely do the risk factors for suicidal thoughts follow those for suicide?
Few prospective studies have investigated social and economic risk factors
for suicide. The magnitude of the increased risk of suicidal thoughts in
relation to marital status, low income, unemployment and substance misuse are
broadly similar to risks associated with these factors and suicide
(Andreasson et al,
1988; Kreitman,
1988; Lewis & Sloggett,
1998; Kposowa,
2000; Qin et al,
2000). We found that associations with measures of poverty
occupational social class, income and housing were greatly attenuated
in models controlling for unemployment (see
Table 4). A similar effect has
been shown in relation to the association of occupational social class with
suicide in a UK-based cohort study (Lewis
& Sloggett, 1998). These findings indicate that the adverse
effects of poverty on suicide risk might be mediated by unemployment and
greater job insecurity among those from poorer backgrounds.
Gender patterns of suicide and suicidal thoughts differ markedly. Although male rates of suicide exceed female rates by approximately 3:1 (Kelly & Bunting, 1998), the incidence of suicidal thoughts is around 30% higher in women than in men. There are a number of possible explanations for the gender differences in suicide and suicidal thoughts. First, they may reflect contrasting prevalences of protective factors, such as social support and help-seeking, in men and women. Several studies indicate that men are less likely than women to seek medical help for psychological problems and prior to suicide (Olfson & Klerman, 1992; Foster et al, 1997; Biddle et al, 2004). Second, risk factors or protective factors may have different effects in men and women (Qin et al, 2000). Finally, as men tend to use more lethal methods of suicide (firearms, hanging) than women (overdose), gender differences in fatality rates following suicide attempts may contribute to the gender differences in suicide (Appleby, 2000).
The different age patterns of suicide and suicidal thoughts are similarly striking. Rates of suicide are lowest among those aged 1624 years (Kelly & Bunting, 1998), the incidence of suicidal thoughts is highest in men and women in this age group. Not only is the incidence of suicidal thoughts highest in the youngest age group, but so too are rates of recovery (although this latter effect was weak). This difference in the age patterning between suicidal thoughts and suicide is similar to the discordance in the age patterning between deliberate self-harm and suicide (Hawton et al, 1997). Perhaps suicidal thoughts, and consequent impulsive actions, are an indicator of the rapid mood swings and changes in life circumstances that surround the move from childhood to young adult-hood. Their transience means not only that they may be less likely to result in carefully planned (and therefore successful) suicide but also that detection of suicide risk and suicide prevention in this age group is particularly challenging.
Suicidal thoughts and suicide prevention
The annual incidence of suicidal thoughts in this survey (approximately 2%)
is around 200 times higher than the annual incidence of suicide (1 per 10 000:
Department of Health, 2002).
This indicates that high-risk approaches to prevention based simply on the
detection and management of all those experiencing suicidal thoughts as
defined in this study would be extremely inefficient unless accompanied by
sophisticated understanding of the factors that exacerbate risk. It is
therefore important to understand the pathways (protective and precipitating)
linking suicidal thoughts to completed suicide. Factors important in such
pathways are likely to be those associated with recovery from suicidal
thoughts (see above), help-seeking behaviours and the recognition and
treatment of those at risk of suicide by health care professionals.
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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 January 7, 2004. Revision received June 10, 2004. Accepted for publication July 9, 2004.