IDENTIFICATION OF SUICIDE RISK FACTORS USING EPIDEMIOLOGIC STUDIES

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Epidemiology is the study of health and illness in human populations.62 Descriptive epidemiologic studies provide information on the scope and impact of disease by examining patterns of the occurrence and distribution of diseases and other health-related outcomes in populations according to sociodemographic characteristics, such as age, gender, race, social class, geographic area, and time.57 The data from such studies complement descriptive findings from clinical observations, basic research, and other sources of information, and are used to generate causal hypotheses. Causal hypotheses are tested in analytic epidemiologic studies, which examine the relationships between risk factors, or antecedent exposures, and health outcomes.62 A major contribution of epidemiologic studies of both clinical and community populations is not only to identify independent risk or protective factors, but also to quantify the strength of their relative contribution to the risk of disease or disorder.79

Epidemiology has played an important role in identifying and determining the potency of risk factors for complex outcomes such as suicide and suicidal behaviors. The past decade, for example, has seen the emergence of the psychological autopsy study as a powerful tool in the methodologic repertoire available to suicidologists. These highly rigorous, population-based studies have been invaluable both in verifying causal hypotheses generated from clinic-based observational studies, in providing additional data on completed suicide that are generalizable to the population, and in generating further causal hypotheses that can be tested by basic, clinical, and epidemiologic research. Similarly, epidemiologic surveys of unbiased samples are able to reach beyond the limits of clinical and other service settings to provide information on the scope of suicidal behaviors and risk factors in the general population. Because population-based research avoids the biases and lack of generalizability associated with nonepidemiologic studies of self-selected clinical populations, 32 and provides findings that are generalizable beyond the study sample, this review focuses primarily on the findings from recent psychological autopsy studies and epidemiologic surveys, particularly those that used standardized psychiatric criteria (e.g., DSM-III-R).1

Increasingly rigorous research efforts, such as the application of multivariate models to test causal hypotheses of both completed and attempted suicide, have expanded scientific understanding of the multiple, interrelated risk factors for suicide. A risk factor is a characteristic, variable, or hazard that increases the likelihood of development of an adverse outcome, 64 which is measurable, and which precedes the outcome.63 The crucial feature of precedence distinguishes risk factors from other characteristics such as concomitants or consequences of outcomes, which are correlates but not risk factors.63

The cause of a complex outcome such as suicidal behavior actually consists of a constellation of components that act together, 99 which vary from one individual to another. From an epidemiologic perspective, and taking into account the distinctive feature of antecedent occurrence, risk factors can be organized within a framework that differentiates between distal and proximal exposures. Distal risk factors represent the foundation upon which suicidal behavior is built. They represent a threshold that increases individual risk for later vulnerability to proximal risk factors. Distal risk factors are not limited to suicide, but can produce multiple adverse physical and mental health outcomes. Their relationship to suicide is fundamental but indirect; they are considered necessary, but not sufficient, for suicide to occur.99 Proximal risk factors, on the other hand, are more closely related temporally to the suicidal event itself, and can act as precipitants. Such “triggering” events are likely to differ with age, gender, ethnicity, and other sociodemographic factors. In and of themselves, proximal risk factors are neither necessary nor sufficient for suicide. The combination of powerful distal risk factors with proximal events and characteristics, however, can lead to the necessary and sufficient conditions for suicide.

The conceptual distinction between distal and proximal risk factors assumes practical importance when planning prevention programs because the strategies used, and their potential effectiveness, are likely to differ depending on the nature of the targeted risk factors. On one hand, the complex nature of suicide suggests that complex and elaborate interventions are necessary for prevention; on the other hand, it implies that preventive and treatment interventions can be targeted and tested at a number of points in a theoretical model.

Both distal and proximal risk factors can and do co-occur in individual, family, and environmental domains, and their co-occurrence is likely to be associated with the greatest risk for suicide.47, 65, 66, 93, 108, 111, 112, 119 It is important to note that many individuals may have one or more risk factors and not be suicidal; on the other hand, the likelihood of suicide or suicidal behavior increases with an increasing number of risk factors.

Section snippets

Methodologic Issues

The coding of a death as suicide is relatively uniform in developed countries, making international comparisons possible.124 Most member nations of the World Health Organization currently use the standardized ninth revision of the International Classification of Diseases (ICD-9) 123 to code mortality data. In the United States, national mortality data are compiled on an annual basis from standardized death certificate information submitted by the States to the National Center for Health

Methodologic Issues

The study of nonfatal suicidal behavior has been hampered by the lack of a consistently applied standard nomenclature among investigators, 37, 86 and by the failure to use clear operational definitions when collecting data or reporting on clinical outcomes.79, 86 The need to apply standardized terminology in the study of suicidal behavior was identified in the literature more than 20 years ago 8 but, with few exceptions (e.g., reference 86), has remained largely unaddressed.37, 38, 79

RISK FACTORS FOR COMPLETED AND ATTEMPTED SUICIDES

Most suicidal behaviors occur on a continuum of severity that proceeds from less serious and more prevalent behaviors through increasingly severe and less prevalent behaviors.66, 86 At one end are included behaviors, such as casual ideation without specific plans. These behaviors may progress in some individuals through persistent, intense ideation that includes a plan, self-inflicted injury without intent to die, and, for a very small proportion of persons at the other end of the continuum, to

IMPLICATIONS FOR PREVENTION

The epidemiologic evidence consistently has shown that suicide has multiple, interacting causes, and risk factors that frequently co-occur. Mental disorders, especially mood, personality, and substance use disorders, underlie the vast majority of completed and attempted suicides. Suicide is a complex, long-term outcome that requires complex theoretical models for appropriate study and complex interventions for effective prevention.

The best method for preventing suicide is likely to be one that

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