Impact of case fatality on the seasonality of suicidal behaviour

A number of differences exist between the seasonality of suicide and suicidal behaviour. Case fatality is one index of the relationship between these phenomena. The purpose of this study was to use contemporaneous data to examine the impact of case fatality on the seasonality of suicidal behaviour. All deliberate self-harm (ICD9 E950-58) hospitalisations (DSH) and deaths (suicide) for 1984-93 were extracted from the Western Australia case register (N = 22 883). Case fatality was calculated by method of suicide. Data were arranged in time series by standardised month according to case fatality; sex and age and analysed using spectral analysis. We found that DSH involving low case fatal methods is seasonal with a spring peak (95% confidence interval). The explained variance of the seasonal rhythm increases with age. Suicide involving high case fatal methods is not seasonal. The increase in DSH seasonality with age may be related to a parallel increase in case fatality.