Psychiatric illness, socioeconomic status, and marital status in people committing suicide: a matched case-sibling-control study

Study objective: Suicides cluster in both families and persons with psychiatric disorders and socioeconomic disadvantages. This study compares these factors between suicide cases, their siblings, and population based controls in an attempt to evaluate both the familial and the individual element of these factors. Design: Nested case-control study. Information on causes of death, psychiatric admission, marital status, children, and socioeconomic factors was obtained from routine registers. Setting: Denmark. Participants: 985 suicide cases, 1104 sex-age (+/- 3 years) matched siblings, and 16619 controls. Main results: The suicide rate ratios obtained from the case-sibling and the case-control analysis, respectively, were of similar magnitude. For example, in the case-sibling analysis the adjusted suicide rate ratios associated with discharge from a psychiatric hospital within the previous 365 days, being unemployed the previous year, having a postgraduate degree and being single were 42.13 (95% CI 17.75 to 100.02), 1.78 (1.35 to 2.36), 0.51 (0.21 to 1.26), and 2.69 (1.91 to 3.79), respectively. The corresponding rate ratios obtained from the case-control analysis were 47.91 (35.41 to 64.83), 1.76 (1.49 to 2.08), 0.45 (0.26 to 0.76), and 2.39 (1.87 to 3.07). Moreover, the analogous ratios when comparing siblings and controls were 1.98 (1.08 to 3.63), 1.22 (1.06 to 1.41), 0.65 (0.44 to 0.95), and 0.89 (0.75 to 1.06). Conclusions: People who commit suicide deviate similarly from siblings and controls in exposure to hospitalised psychiatric disorders and socioeconomic disadvantages, although these factors contribute to the familial aggregation of suicides.