Suicide

Human beings engage in a wide range of self-injurious thoughts and behaviors. These range from risk taking (e.g., skydiving), through suicide ideation, instrumental suicide-related behavior (e.g., suicide threats) to suicidal acts (attempted and completed). Suicide involves self-chosen behavior intended to bring about one's death in the shortest term. Each year, at least half a million people worldwide end their own lives. Difficulties in identifying unequivocal evidence of intent underpin the generally accepted view that official statistics underestimate the true suicide rate by an unknown amount. The presence of a note or letter often provides the clearest evidence of intent, but less than 30% of those who die by their own hand leave such a communication. Differing legal and ascertainment procedures account for some of the variation in national suicide rates. There may also be social pressures to underreport, especially in the absence of unequivocal evidence of intent, because of the stigma associated with suicide. In doubtful circumstances, attributing the cause of death to something other than suicide may lessen the pain for family and friends. Defining attempted suicide is equally complex because the behavior is characterized by several dimensions, including the lethality of the method used, the level of medical injury inflicted, and the level of suicidal intent. In North America, evidence of intent is included in the definition of attempted suicide. In Europe, evidence of intent is of lesser importance in acknowledgment of the fact that divergent intentions may lead to a suicide attempt. Definitional variations contribute to an unknown extent to discrepancies among research findings on suicide and attempted suicide in different countries.

As a cause of death, suicide is one of the least understood. Those who attempt or complete suicide share a number of general characteristics or risk factors, including major depression, alcohol dependence, substance abuse, antisocial behavior, childhood abuse, and personality disorder. The majority of risk factors for suicidality (the occurrence of suicidal thoughts or behaviors) have been identified through retrospective studies, and the false-positive rate—the probability of wrongly inferring a link between a particular factor and suicide risk—is very high for this method of inquiry. This is because retrospective inquiries are prone to hindsight bias: Knowing the outcome of an event increases the post hoc estimate of the perceived likelihood of the outcome. Given an account of a person's life history and told that the person committed suicide, people are more likely to infer links between factors in the person's biography that might explain the cause of death than are those who are given the same account and asked to predict the likelihood of suicide. Knowing the outcome approximately doubles the likelihood of a perceived connection between an event in the person's life history and his or her cause of death.