Department of Psychology, Harvard University, Massachusetts, USA
Department of Epidemiology, National Institute of Psychiatry and Universidad Autonoma Metropolitana, Mexico City, Mexico
Department of Psychiatry, State University of New York, Stony Brook, USA
Health Services Research Unit, Institut Municipal d'Investigacio Medica IMIM, Barcelona, Spain
University of Leipzig, Department of Psychiatry, Leipzig, Germany
Christchurch School of Medicine & Health Sciences, New Zealand
Department of Neurosciences and Psychiatry, University Hospitals, Gasthuisberg, Belgium
Department of Health Care Policy, Harvard Medical School, Boston, Massachusetts, USA
Department of Mental Health, AUSL di Bologna, Bologna, Italy
Ukrainian Psychiatric Association, Kyiv, Ukraine
Netherlands Institute of Mental Health and Addiction, Utrecht, The Netherlands
Department of Psychiatry, University College Hospital, Ibadan, Nigeria
Sant Joan de Deu-SSM, Barcelona, Spain
Institute of Mental Health, Peking University, People's Republic of China
Department of Psychiatry and Psychology, St George Hospital University Medical Center, Beirut, Lebanon
Department of Psychology, Harvard University, Massachusetts, USA
Hospital Fernand Widal, Paris, France
Research and Planning, Mental Health Services, Ministry of Health, Jerusalem, Israel
Department of Epidemiology, National Institute of Psychiatry and Universidad Autonoma Metropolitana, Mexico City, Mexico
Keio University, Tokyo, Japan
Colegio Mayor de Cundinamarca University, Saldarriaga Concha Foundation, Bogota, Colombia
Harvard University School of Public Health, Boston, Massachusetts, USA.
Correspondence: Matthew K. Nock, PhD, Department of Psychology, Harvard University, 33 Kirkland Street, 1280 Cambridge, MA 02138, USA. Email: nock{at}wjh.harvard.edu
None. Funding detailed in Acknowledgements.
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Suicide is a leading cause of death worldwide; however, the prevalence and risk factors for the immediate precursors to suicide – suicidal ideation, plans and attempts – are not wellknown, especially in low- and middle-income countries.
Aims
To report on the prevalence and risk factors for suicidal behaviours across 17 countries.
Method
A total of 84 850 adults were interviewed regarding suicidal behaviours and socio-demographic and psychiatric risk factors.
Results
The cross-national lifetime prevalence of suicidal ideation, plans, and attempts is 9.2% (s.e.=0.1), 3.1% (s.e.=0.1), and 2.7% (s.e.=0.1). Across all countries, 60% of transitions from ideation to plan and attempt occur within the first year after ideation onset. Consistent cross-national risk factors included being female, younger, less educated, unmarried and having a mental disorder. Interestingly, the strongest diagnostic risk factors were mood disorders in high-income countries but impulse control disorders in low- and middle-income countries.
Conclusion
There is cross-national variability in the prevalence of suicidal behaviours, but strong consistency in the characteristics and risk factors for these behaviours. These findings have significant implications for the prediction and prevention of suicidal behaviours.
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The purpose of the current study was to estimate the cross-national prevalence of suicidal behaviours and to examine risk factors for these outcomes using data from the World Health Organization (WHO) World Mental Health (WMH) Survey Initiative.10 Several studies have provided valuable information about suicidal behaviours across several countries.5,11,12 The current study extends prior work by conducting a more thorough examination of suicidal behaviours, using more consistent assessment methods across sites, and represents the largest, most representative examination of suicidal behaviours ever conducted.
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Procedures
All respondents completed a Part I interview that contained core diagnostic
assessments, including the assessment of suicidal behaviours. All Part I
respondents who met criteria for any disorder and a subsample of approximately
25% of the remainder of the respondents were administered a Part II interview
that assessed potential correlates and disorders of secondary interest
(n=48 427). Data were weighted to adjust for this differential
sampling of Part II respondents, differential probabilities of selection
within households, and to match samples to population socio-demographic
distributions.
Standardised interviewer training procedures, WHO translation protocols for all study materials, and quality control procedures for interviewer and data accuracy that have been consistently employed across all WMH countries are described in more detail elsewhere.10,15,16 Informed consent was obtained before beginning interviews in all countries. Procedures for obtaining informed consent and protecting individuals were approved and monitored for compliance by the institutional review boards of organisations coordinating surveys in each country.
Measures of suicidal behaviours
Suicidal ideation, plans and attempts were assessed using Version 3.0 of
the WHO Composite International Diagnostic Interview
(CIDI).16 The
computer-assisted WMH–CIDI (for Windows) was used in countries where it
was financially and logistically possible to do so; elsewhere, the
paper-and-pencil version was used. Based on evidence that reports of such
potentially embarrassing behaviours are higher in self-administered than
interviewer-administered
surveys,17 these
questions were printed in a self-administered booklet and referred to by
letter (e.g. `Did experience C ever happen to you?'; in booklet, `C=You
attempted suicide'). If the respondent was unable to read, the interviewer
read these items aloud (19.5% of all instances). Interviews assessed the
lifetime presence and age-of-onset of each outcome.
Risk factors for suicidal behaviours
Interviews also examined three sets of risk factors for suicidal
behaviours: socio-demographics, characteristics of suicidal behaviours and
temporally prior DSM–IV mental disorders (i.e. those with an onset prior
to the first onset of suicidal ideation). The socio-demographic factors
included gender, age/cohort, education, employment history, and marital
history. Characteristics of suicidal behaviours included age-of-onset of
ideation, time since onset of ideation, presence of a suicide plan and time
since onset of plan. Respondent disorders were assessed using the WHO
CIDI.16 The
assessment included DSM–IV mood, anxiety, impulse control and substance
use disorders. Prior studies using clinical reappraisal interviews have found
CIDI diagnoses to have good concordance with blinded diagnoses based on the
Structured Clinical Interview for
DSM–IV18 in
probability subsamples of respondents from the surveys in France, Italy, Spain
and the
USA.19,20
Statistical analysis
Cross-tabulations were used to estimate lifetime prevalence of suicidal
ideation, plans and attempts. Discrete-time survival analysis with person-year
as the unit of analysis and including both stable (e.g. gender) and
time-varying (e.g. marital history)
covariates21 was
used to study retrospectively assessed risk factors for the first onset of
each suicidal behaviour. Discrete-time survival analysis uses each year of
life of each respondent as a separate observation, so that a sample of 100 000
respondents with an average age of 30 years would be treated as 3 million
separate records. Each record is coded for the respondent's stable
characteristics (e.g. gender), the respondent's age at the time of the
observational record (e.g. the 20th year of a respondent's life who was age 45
years at the time of interview), values on the time-varying predictors as of
that year of life (e.g. whether or not the respondent was still a student, had
ever been married, and had ever been employed as of age 20), and values on the
outcomes as of that year (e.g. whether or not the respondent had ever made a
suicide attempt and, if so, whether this was the year of the respondent's
first lifetime attempt). The data file was analysed to compare person-years
for all respondents that had never had the outcome of interest v. the
year of first onset of the outcome using a logistic regression modelling
approach and controlling for person-year (i.e. age at the time of the
observational record) as well as for the predictors. Logistic regression
coefficients were converted to odds ratios (ORs) for ease of interpretation
and 95% confidence intervals (CIs) are also reported and have been adjusted
for design effects. Continuous variables were divided into categories to
minimise effects of extreme values. Standard errors (s.e.) and significance
tests were estimated using the Taylor series
method22 using
SUDAAN software23
(for UNIX) to adjust for the effects of weighting and clustering. Multivariate
significance was evaluated using Wald
2-tests based on
design-corrected coefficient variance–covariance matrices. Statistical
significance was evaluated using two-tailed 0.05-level tests.
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Within-country prevalence estimates show substantial variability, with the cross-national estimate outside the 95% CI in 13 of the 17 countries for suicidal ideation, and 12 of the 17 for suicide plans and attempts. Prevalence estimates in low- and middle-income countries are similar to those in high-income countries for: suicidal ideation (3.1–12.4% v. 3.0–15.9% respectively), suicide plan (0.9–4.1% v. 0.7–5.6% respectively) and suicide attempt (0.7–4.7% v. 0.5–5.0% respectively). Although prevalence estimates varied cross-nationally, the conditional probability of suicide plan and attempt among ideators is more consistent across countries, with the cross-national estimate outside the 95% CI in only 5 of the 17 countries for plans, 7 of 17 countries for attempts, 9 of 17 countries for unplanned attempts, and 4 of 17 countries for planned attempts.
Socio-demographic factors
In the cross-national sample, risk of each suicidal behaviour is
significantly related to being female, younger age, having fewer years of
formal education, and before ever being married
(Table 1). The ORs of these
predictors are fairly modest in magnitude (OR=1.3–3.1) with the
exception of age. Age is inversely related to risk of each suicidal behaviour,
with ORs increasing as age decreases (50–64 years, OR=2.6–3.4;
35–49 years, OR=4.2–5.6; 18–34 years, OR=9.5–12.4).
Employment history is unrelated to suicidal behaviours. Notably, the relations
between the socio-demographic risk factors and suicidal behaviours are
attenuated when predicting suicide plans and attempts among ideators
(Table 2), suggesting the
relations between these socio-demographic factors and suicide plans and
attempts are due primarily to their association with suicidal ideation.
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Table 1 Socio-demographic risk factors for first onset of suicide-related outcomes:
pooled analysis (n=48 427).
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Table 2 Socio-demographic risk factors for first onset of suicide-related outcomes
among ideators: pooled analysis.
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Within-country findings are very similar to those in the pooled sample. For example, a dominant sign pattern exists for female gender and risk of the three main outcomes of suicidal ideation, plan and attempt (i.e. 47 of the 51 ORs across the 17 separate countries are 1.0 or greater) and 57% of the within-country ORs for gender are significant at the 0.05 level. Odds ratios for female gender are always 1.0 or greater for suicidal ideation, and are less than 1.0 in only two instances for suicide plan (Japan 0.9, Nigeria 0.9) and two instances for attempt (Colombia 0.9, Nigeria 0.8), none being statistically significant. Similarly, the strong relation between age and risk of suicidal behaviours is consistent across 16 of the 17 countries (in Japan the highest risk of each outcome is in the 35–49 years cohort), with 88% of the within-country ORs for the youngest cohort significant at the 0.05 level. Results are similar but less consistently significant in within-country analyses for education, employment and marital history given the relatively small effect sizes for these relations.
Characteristics of suicidal behaviours as risk factors
Suicide ideators within each country were classified into terciles based on
age-of-onset of suicidal ideation to examine the relation between age-of-onset
and risk of transition from ideation to plans and attempts. Analyses revealed
that earlier age-of-onset is significantly associated with greater risk of
suicide plan and attempt among those with ideation
(Table 2). Importantly, the
transition from suicidal ideation to first onset of plan or attempt is
extremely elevated within the first year of onset of ideation
(OR=117.4–123.1), and decreases substantially thereafter
(OR=1.5–4.4). Among ideators, having a suicide plan is associated with a
significantly higher risk of making an attempt (OR=7.5), although the odds of
making an unplanned attempt within the first year after onset of ideation are
just as high (OR=174.6) as the odds of making an attempt within the first year
after onset of a plan (OR=168.4). Thus, whether a plan is present or not, the
highest risk of suicide attempt is in the first year after onset of
ideation.
Examination of age-of-onset curves reveals that across all 17 countries the risk of first onset of suicidal ideation increases sharply during adolescence and young adulthood (online Fig. DS1). These curves separate in the mid-teens to early 20s, with several countries (Japan, New Zealand, USA) showing an earlier increase in risk of suicidal ideation, while other countries have a sharp increase in risk later in life (Israel, Mexico, Spain, Ukraine). Conditional age-of-onset curves show that the rapid transitions from ideation to attempt (online Fig. DS2) occur within the first year of onset of ideation more than 60% of the time across all 17 countries. The same pattern was observed for the transitions from ideation to plan and plan to attempt across all countries.
Mental disorders as risk factors
In the cross-national sample, the presence of a prior mental disorder is
associated with significantly increased risk of suicidal behaviours, even
after controlling for socio-demographic factors, characteristics of suicidal
behaviours, and country of residence (Tables
3 and
4). Relations are strongest
across both high-, and low- and middle-income countries for mood disorders
(OR=3.4–5.9) and impulse-control disorders (OR=3.3–6.5), followed
by anxiety disorders (OR=2.8–4.8) and substance use disorders
(OR=2.8–4.6). Importantly, associations between mental disorders and
suicidal behaviours are attenuated when predicting plans and attempts among
ideators, with ORs decreasing to 1.0–2.1 across all categories. Among
ideators, the risk of making an attempt is highest for those with substance
use and impulse-control disorders, suggesting that these disorders are most
strongly associated with acting on suicidal thoughts when they are present.
Results also show a strong dose–response relationship between the number
of mental disorders present and the risk of suicidal behaviours.
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Table 3 High-income countries: DSM-IV disorders as risk factors for first onset of
suicide-related outcomes (pooled analysis).
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Table 4 Low- and middle-income countries: DSM–IV disorders as risk factors
for first onset of suicide-related outcomes (pooled analysis).
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In within-country analyses, the presence of any mental disorder is associated with significantly increased risk in each of the 17 countries. The ORs for these analyses are quite stable, with only three countries differing significantly from the cross-national estimate for any outcome. Specifically, Israel is above the cross-national estimate for ideation, plan, and attempt, Italy is above the estimate for attempt, and Germany is below the estimate for ideation. The strong dose–response relationship between number of disorders and risk of suicidal behaviours is also consistent across all 17 countries.
Within-country analyses examining the relationship between each of the four disorder categories and the three primary suicidal behaviours also are largely consistent with those in the pooled cross-national sample, with only 3 of 204 ORs (1.5%) less than 1.0, and 92.5% of ORs significant at the 0.05 level. The greatest variability among countries is in the relation between mood disorder and suicidal behaviours. Seven countries have ORs significantly higher than the cross-national estimate (Belgium, China, Germany, Israel, Italy, Japan and Nigeria), with two countries (Colombia, France) below the cross-national estimate.
Analyses revealed an interesting pattern regarding low- and middle-income v. high-income countries. In high-income countries the presence of a mood disorder is the strongest predictor of suicidal ideation, plan and attempt (Table 3; 9 of 10 countries show this pattern). However, in low- and middle-income countries the presence of an impulse-control disorder is a stronger predictor than mood disorder (Table 4; 5 of the 6 countries in which impulse-control disorders were examined). Thus, although the presence of mental disorders in general, and comorbidity in particular, are consistently strong predictors of suicidal behaviours cross-nationally, there are notable differences in the type of disorder most strongly predictive of suicidal behaviours.
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Limitations
Several important limitations should be borne in mind when interpreting
these results. First, although the overall response rate was at an acceptable
level, response rates varied across countries and in some cases were below
commonly accepted standards. We controlled for differential response using
post-stratification adjustments, but it is possible that response rates were
related to the presence of suicidal behaviours or mental disorders, which
could have biased cross-national comparisons. Also, although surveys in most
countries included nationally representative samples, several surveys (e.g.
China, Japan) focused on specific urban areas and so findings from those
surveys may not generalise to all regions of those countries. A related
limitation is that although we examined suicidal behaviours across 17
countries, several countries/regions with high rates of suicide, such as India
and South East Asia, were not
included.24 The
inclusion of data from additional countries/regions in future work will
significantly enhance our understanding of the factors influencing suicidal
behaviours further.
Second, data were based on retrospective self-report of the occurrence and timing of suicidal behaviours, and thus may be subject to underreporting and biased recall. We also did not collect information from third-party informants to validate respondent reports. On balance, several systematic reviews have demonstrated that adults can recall past experiences with sufficient accuracy to provide valuable information,25,26 and such data are especially useful when prospective data are not available,27 as in the current case. Another limitation is that there may be cultural differences in the willingness to report on suicidal behaviours and in the interpretation of questions about DSM–IV mental disorders. Our results must be viewed with these limitations in mind.
Third, several mental disorders were not adequately assessed in the WMH surveys for various reasons. A few DSM–IV disorders were not assessed in some surveys because they were believed to have low relevance or they were excluded from analyses owing to an insufficient number of cases, such as impulse-control disorders in Nigeria. In some cases, disorders were not adequately assessed owing to skip logic errors, such as bipolar disorder and substance use disorders in the European Study of the Epidemiology of Mental Disorders surveys.10 Schizophrenia and other nonaffective psychoses were not included in any WMH survey because previous validation studies showed they are overestimated in lay-administered interviews like the CIDI.28 These exclusions are unfortunate because prior research clearly indicates that bipolar and substance use disorders are strongly associated with suicidal behaviours,3,6 suggesting that schizophrenia and suicidal behaviours share unique prevalence patterns and are strongly related in low- and middle-income countries;29 thus, the current study might have provided important information in this regard. The measurement of these disorders and the explanation of their relationship to suicidal behaviours in both high-income and low- and middle-income countries is one of the most important tasks for future work on this topic.
Fourth, this initial study included only a limited range of risk factors for suicidal behaviour. Factors such as individual Axis I and Axis II disorders, and traumatic life events were not examined in this study. Also excluded were potential protective factors such as treatment utilisation and social support. The investigation of these and other factors remain important directions for future research.
Clinical implications and future research
These limitations notwithstanding, several important findings from this
study warrant more detailed comment. Perhaps the most important finding of
this study is that there is strong cross-national consistency for several key
risk factors for suicidal behaviours. Female gender, young age, and low
educational attainment have been identified as risk factors for suicidal
behaviours in prior
studies,3,6
and the current findings suggest these risk factors may be universal. Future
research is needed to determine whether risk of suicidal behaviours is
occurring at higher rates among young people, or whether people simply become
less likely to report on earlier suicidal behaviour with age, due to
forgetting or re-interpretation of these earlier events.
Risk of suicide plans and attempts was also highest within the first year of ideation and when suicidal ideation had an earlier age-of-onset. Remarkably, 60% of the transitions from ideation to attempt – as well as from ideation to plan and plan to attempt – occur within the first year of onset of ideation and this result is consistent across all 17 countries. Few studies have examined the probability and speed of transition from ideation to plans and attempts, and this information can be especially useful to healthcare providers. Another important finding is that the strong relationship observed between mental disorders and suicide plans and attempts diminishes when controlling for ideation. Thus, although mental disorders are strong risk factors for suicidal behaviours, factors beyond the mere presence of mental disorders explain the transition from ideation to plans and attempts.
Several recent studies have suggested that mental disorders are less important in the occurrence of suicidal behaviours in low- and middle-income countries relative to high-income countries. Whereas studies in high-income countries suggest that >90% of those who die by suicide have a diagnosable mental disorder and >60% have a mood disorder in particular,30 rates in low- and middle-income countries have been suggested to be as low as 60% and 35% respectively.7 Our results indicate that when the same assessment methods are used cross-nationally, mental disorders are as predictive of suicidal behaviours in low- and middle-income countries as they are in high-income countries, and that comorbidity is an important predictor across all countries. Notably though, impulse-control disorders were stronger predictors than mood disorders in most low- and middle-income countries. The fact that mood and impulse-control disorders have the strongest associations with suicidal behaviours is consistent with prior work highlighting the importance of depressed mood and impulsiveness in the suicidal process,31 and extends these findings cross-nationally. The reason for the difference in the importance of impulse-control disorders between high-income and low- and middle-income countries is unclear and awaits further examination.
Future research must examine factors that might explain the variability in prevalence and must also develop more complex risk and protective models that take into account both common and specific factors for each country/region. From a practical perspective, the similarities observed between low- and middle-income and high-income countries suggest equivalent resources should be devoted to studying and preventing suicidal behaviours in these countries. Currently, resources devoted to the treatment of mental disorders in general, and to suicide prevention in particular,9 are lacking in many low- and middle-income (and high-income) countries.7,10 It is important to note, however, that more treatment alone is not the answer. Several recent studies have highlighted that despite significant increases in service utilisation among suicidal individuals, the rates of suicidal ideation, plans and attempts have remained virtually unchanged.4 Moreover, although several different forms of treatment have proven effective at decreasing the likelihood of making suicide attempts, psychosocial treatments have proven less effective at decreasing the likelihood of death by suicide.32 Improvements in our ability to predict and prevent suicidal behaviours and suicide deaths are clearly needed, and require that we continue to identify the risk and protective factors that influence such behaviours. In addition, we need to develop more sophisticated methods for synthesising and using the information obtained about such factors.
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