Journal of Affective Disorders 71 (2002) 51–59 www.elsevier.com / locate / jad Research report Seasonal variation in specific methods of suicide: a national register study of 20 234 Finnish people a, a a b,c * ¨¨ ¨ Pirkko Rasanen , Helina Hakko , Jari Jokelainen , Jari Tiihonen a Department of Psychiatry, University of Oulu, Peltolantie 5, FIN-90220 Oulu, Finland b Department of Forensic Psychiatry, University of Kuopio, Niuvanniemi Hospital, FIN-70240 Kuopio, Finland c Department of Clinical Physiology, Kuopio University Hospital, FIN-70240 Kuopio, Finland Received 6 February 2000; accepted 27 April 2001 Abstract Background: Previous studies have suggested differences in seasonal variation of violent and non-violent suicides, but seasonal distribution of the specific methods of suicide is less clear. Method: We investigated the seasonal distribution of the specific suicide methods for both genders during a 16-year period. The seasonal effect was explored by monthly ratio statistics from the large population-based data including all suicides in Finland during years 1980–1995 ( n 5 20 234). Results: Hanging peaked in spring among both genders. In summer, the significant peaks were occurred in suicides by drowning, jumping and gassing among males. The bimodality in female suicides with autumn peaks was explained by poisoning and drowning. Traffic suicides showed substantial winter-troughs for both genders. Conclusions: The results suggested that specific violent and nonviolent methods of suicides grouped into their traditional clusters on the basis of their seasonality, except suicides by gassing and shooting. The seasonal distribution in specific suicide methods should take into account in suicide prevention at clinical work and also it should be considered while determining which methods of suicides are regarded as violent or non-violent methods in research.  2002 Elsevier Science B.V. All rights reserved. Keywords: Suicide; Method; Violent; Non-violent 1. Introduction also shown to be a gender-specific phenomenon. For males, the major peaks occur in spring and early A seasonal variation in suicides has been reported summer with troughs in winter (Chew and in several studies (Kevan, 1980; Skutsch, 1981; McCleary, 1995; Hakko et al., 1998a; Preti and Maes et al., 1993; Chew and McCleary, 1995). It has Miotto, 1998). Correspondingly, there exists a bimodal distribution among females with peaks in ¨ ¨ spring and autumn (Meares et al., 1981; Nayha, *Corresponding author. Tel.: 1 358-8-315-7011; fax: 1 358-8- 1982; Lester and Frank, 1988; Micciolo et al., 1989; 315-7485. ¨¨ E-mail address: pirkko.rasanen@oulu.fi (P. Rasanen). Hakko et al., 1998b). 0165-0327 / 02 / $ – see front matter  2002 Elsevier Science B.V. All rights reserved. PII: S0165-0327(01)00411-6