In this nationally representative urban sample of respondents from Mexico, we found that a psychiatric disorder was present in 48.8% of those with a suicide ideation and in 65.2% of those with an attempt. Although all disorders were associated with increased odds of a subsequent suicide attempt in bivariate models, more elaborate multivariate models that adjusted for comorbidity suggested that conduct disorder and alcohol abuse or dependence were the most important predictors in this sample, increasing the likelihood of an attempt by about six times. Other individual disorders, mainly anxiety disorders, followed in the list of predictors with increasing ORs of about 2–3 fold. In multivariate models, mood disorders produced increased but non-significant ORs for suicide attempt. Most associations of psychiatric disorders with suicidality were due to the prediction of suicidal ideation. Very few disorders accounted for the transition between ideation and a suicide plan (only oppositional-defiant disorder and alcohol abuse or dependence), or between ideation and planned attempt (only conduct disorder) and between ideation and unplanned attempt (conduct disorder reduced the risk and general anxiety disorder increased it). The inverse association between conduct disorder and unplanned attempts is surprising and we recommend caution in weighting this finding too heavily given that the seven other associations between conduct disorder and suicidal behaviors tested in this study were all positive and consistently among the strongest ORs observed in this study. Results suggested that interventions to reduce psychiatric disorders would have a high impact on suicide ideation (76% reduction) and attempts (73% reduction).
This study in a developing country confirms findings from psychological autopsy studies on the high prevalence of psychiatric disorders among those with a suicide attempt, suggesting that psychiatric disorders should be target for suicidal interventions even in countries where low socioeconomic status and unemployment have been pointed as key risk factors (Ortiz-Hernandez et al., 2007
). The prevalence of psychiatric disorders among suicide attempters in Mexico is lower than the prevalence reported in the US (79.6%)(Nock et al., 2009a
); however, this maybe due to the overall higher prevalence of psychiatric disorders in the US compared to Mexico (Demyttenaere et al., 2004
; Nock et al., 2009a
) and not to a low relative risk associated with psychiatric disorders in Mexico.
Our analyses replicate the findings from a prior study in the US (Nock et al., 2009a
), showing that bivariate associations of psychiatric disorders with suicidality are limited because there are large effects of comorbidity on individual disorders. The current study extends earlier work by illuminating the larger role that conduct disorder and alcohol use disorder play in the onset of suicidal behavior among Mexicans. Other reports from individual developing countries participating in the WMH Surveys (Demyttenaere et al., 2004
) also have found larger than expected roles of impulse-control, substance use, and anxiety disorders in the onset of suicidal behavior in South Africa (Joe et al., 2008
), Nigeria (Gureje et al., 2007
), Ukraine (Bromet et al., 2007
), and Israel (Levinson et al., 2007
). In China, more consistent with reports from developed Western countries, mood and anxiety disorders have emerged as the strongest diagnostic predictors of suicidal behavior (Lee et al., 2007
). On the other hand, in developed European countries participating in the WMH Surveys (Bernal et al., 2006) depression, dystimia, GAD and PTSD were the disorders more related to suicide ideation and attempt. Whether this series of results will hold in these individual countries when more complex models are used is a matter for future work, but merged data from the WMH Surveys suggest that, as a group, in developing countries other disorders were stronger predictors of suicide attempts including: conduct disorder, oppositional-defiant disorder, intermittent-explosive disorder, drug and alcohol abuse, and PTSD (Nock et al., 2009b
). The reasons for this difference in the risk of individual disorders in developed and developing countries are not known and represent an important direction for future suicide research.
The risk for suicide attempt was strongly related to the number of disorders, as previously reported (Beautrais et al., 1996
, Kessler et al., 1999
, Nock et al., 2008
). As in the US sample (Nock et al., 2009a
), the current analyses add to the literature in showing that despite this strong dose-response relation, sub-additive interactive effects were observed, suggesting that there is a decay in the predictive power of comorbidity as the number of comorbidities gets larger. Analysis of possible factors associated with these large levels of comorbidity, such as increasing levels of stress and large amounts of negative lifetime experiences that may lead to a high likelihood of suicidal behavior will be future topics of our inquiries. Whether the dose-response found for number of disorders and risk of suicidality could be applied to completed suicide is a matter of further discussion, beyond the scope of this report. Nevertheless, some caution for simple generalization of our findings is needed, since at least one recent report on psychiatric comorbidity and risk of completed suicide failed to find a similar dose-response as reported here (Walby et al., 2006).
While risk factor analyses pointed to substance use and impulse-control disorders as the main psychiatric disorders to consider in Mexico, PARP results shifted the focus to anxiety and mood disorders. This is consistent with the similar ORs observed among several disorders in this report () and to the fact that anxiety disorders have, overall, much higher prevalence in Mexico than other psychiatric disorders (Medina-Mora et al., 2007
, Medina-Mora et al., 2005
). The complex picture of diverse psychiatric disorders impacting on suicidality in Mexico, both on clinical and public health practice, needs to be carefully considered when implementing preventive strategies in the country. Although it is clear that suicide prevention efforts should include a focus on screening and treating psychiatric disorders in both developed and developing countries, simply translating experiences and manuals for public health control of suicidality from other, usually developed nations, does not seem appropriate in the light of these results.
The study findings must be evaluated in the context of several study limitations. First, the M-NCS is a household survey that excluded homeless and institutionalized people, both populations known to have high prevalence of suicidal behavior (Desai et al., 2003
). Second, the diagnostic instrument used in the M-NCS did not include an assessment of all DSM-IV disorders, some of which have been linked to increased risk of suicidal behaviour and increase the comorbidity discussed here, such as schizophrenia and other non-affective psychoses (Harkavy-Friedman et al., 2004
; Kessler et al., 1999
). Third, validity and reliability data were not obtained on the measures of ideation, plans and attempts. Fourth, although we examined suicide ideation, plans, and attempts, we did not measure other important self-injurious behaviors such as suicide gestures (e.g., Nock and Kessler, 2006
) and non-suicidal self-injury (e.g., Nock and Prinstein, 2005
), and so the epidemiology of these outcomes awaits further study. Fifth, we did not examine the severity and/or recency of disorders in these models and whether these factors could help explain some (but not all) of the findings regarding the transitions from ideation to attempt. Finally, these analyses used data on retrospectively reported ages of onset that are subject to recall errors, which likely lead the results reported here to be conservative with regard to the magnitude of the problem of nonfatal suicide-related outcomes in Mexico.