Seasonality of suicide: relationship with the reason for suicide

This study set out to test the hypothesis that the suicides that can be attributed to a psychiatric illness show a higher seasonality than the suicides due to any other reason.

All the suicides registered in Italy from 1984 to 2000 (57,796 deaths by suicide: males = 41,741, yearly rate = 11.3 per 100,000; females = 16,055, yearly rate = 4.0 per 100,000) were analyzed with circular statistic techniques, based on the maximization of mean vector length method and on the Rayleigh test.

The suicides clearly attributed to a psychiatric illness were 35.0% among males and 51.3% among females. An economic reason for suicide was more frequently found among males; somatic illness or sentimental reasons were equally distributed in both sexes. The suicides attributable to a psychiatric illness showed a significantly higher seasonal unevenness than the suicides attributable to somatic illness and to sentimental or economic reasons.

The main drawback of this study is that psychiatric diagnoses were not formally assessed by a forensic specialist. However, it succeeded in showing that the dynamics of suicidal behaviour are not unilineal: suicides due to psychiatric or somatic illness mainly happen in spring/summer and those due to economic difficulties mainly in December. Patients with psychiatric and/or somatic illness should be more carefully followed in spring/summer.