title: Season-of-birth as a risk factor for the seasonality of suicidal behaviour.
abstract: Despite implicating the same biological systems, the relationship between suicide seasonality and season-of-birth has not been examined previously. The purpose of this study was to investigate the interaction between season-of-birth and the seasonality of suicidal behaviour. All adult suicides (N = 2923) and deliberate self harm (DSH) hospitalizations (N = 33321) in Western Australia (1970-96) were examined. A variable population at risk approach was used to determine season-of-birth. Seasonality was established by spectral analysis. We found that DSH has a significant season-of-birth (p = 0.047) and seasonality of occurrence, both peaking in spring. Individuals born in the 90 days centred on the peak birth period, however, show no DSH seasonality. In contrast, suicide has no season-of-birth (p = 0.53). We also found a season-of-birth effect among the DSH group that eliminates any seasonality of DSH among the high-risk by birth group. Further work is needed to identify the possible biological and environmental determinants of this interaction.
authors.affiliation: Centre for Clinical Research in Neuropsychiatry, Graylands Hospital, Locked Bag No 1, Claremont, Western Australia, 6901, Australia.
authors.forename: Daniel
authors.initials: D
authors.lastname: Rock
authors.forename: David
authors.initials: D
authors.lastname: Greenberg
authors.forename: Joachim
authors.initials: J
authors.lastname: Hallmayer
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D003430:Cross-Sectional Studies; D005260:Female; D006760:Hospitalization / Q000706:statistics & numerical data; D006801:Humans; D008297:Male; D008875:Middle Aged; D012307:Risk Factors; D012621:Seasons; D013223:Statistics as Topic; D013405:Suicide / Q000523:psychology / Q000706:statistics & numerical data*; D013406:Suicide, Attempted / Q000523:psychology / Q000706:statistics & numerical data*; D014904:Western Australia