Prison inmates are exposed to a number of adverse conditions prior to and during incarceration that place them at risk for suicide. The interpersonal theory of suicide may prove useful in better understanding suicide in prisons, allowing for more effective prevention and treatment programs. However, no studies of the interpersonal theory have been conducted in prison populations. Further, there have been no studies examining the factor structure of the assessment of one of the theory's main constructs: the acquired capability for suicide. The current study examined the factor structure of the Acquired Capability for Suicide Scale in a sample of male prison inmates. We found that a 4-factor model provided the best statistical and conceptual fit, though only 3 of these factors were meaningful with an additional method-factor. The 3 resulting factors were each associated with previous exposure to painful and provocative events, but none differentiated suicide attempter status. Results suggest that the interpersonal theory has promise in application to suicide in prison populations, but more work is needed to develop a self-report measure of acquired capability, particularly as it relates to prisoners.

The interpersonal theory of suicide posits that individuals who experience suicide ideation will only develop suicidal intent, and subsequently engage in suicidal behavior when they have concomitant fearlessness about death and tolerance for physical pain (i.e., the capability for suicide). The current studies examined the hypothesis that one aspect of the capability for suicide—fearlessness of the pain involved in dying—would amplify the positive association between current suicide ideation and a previous suicide attempt in two samples at high risk for experiencing suicide ideation and suicide attempts. Study 1 examined this relation using self-report methods in a sample of adults entering treatment in a mental health outpatient clinic. Study 2 utilized similar methods in a sample of adults admitted to inpatient psychiatry. Both studies indicated that those individuals who reported suicide ideation were more likely than non-ideators to report having attempted suicide only if they also reported greater fearlessness of the pain involved in dying. The current findings support the theorized role of the capability for suicide in the transition from ideation to attempt and also support assessing the capability for suicide in risk assessment.

The interpersonal theory of suicide proposes that the most proximal cause of suicide is the combination of thwarted belongingness and perceived burdensomeness coupled with a pre-existing vulnerability of reduced fear of death and increased pain tolerance. This pre-existing vulnerability develops in response to painful and provocative life events. According to the theory, empirically demonstrated risk factors for suicide operate by increasing the likelihood of one or more of the theory's constructs. The current study examined the relations of the major constructs of the interpersonal theory with suicide case status compared to living controls in the second half of life. The current study used a pre-existing psychological autopsy database to compare suicide decedents to living controls 50 years and older. Theory constructs were measured by composite scores of thwarted belongingness, perceived burdensomeness, and painful and provocative experiences using an a priori selection of items comprising each construct. Suicide decedents experienced greater levels of all three of the theory's constructs when examined independently compared to living controls. When examined simultaneously while also controlling for Major Depression, greater perceived burdensomeness and painful and provocative experiences were associated with suicide case status (vs. control). The interpersonal theory is a comprehensive framework that may be useful in understanding risk for death by suicide in the second half of life. Clinical management of suicide risk for adults in the second half of life could include a focus on perceived burdensomeness, as the IPTS proposes that this psychological state is amenable to change via therapeutic intervention.