Understanding weekly cycles in suicide: an analysis of Austrian and Swiss data over 40 years.

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Seasonal as well as weekly cycles in suicide have been described, replicated and poorly understood for a long time. In Western countries, suicides are typically least frequent on weekends and most frequent on Mondays and Tuesdays. To improve understanding of this phenomenon a strategy is required which focuses on anomalous findings beyond the regular patterns. Here, we focused on instances where the weekly suicide patterns disappear or are interrupted. We used data from Swiss and Austrian mortality statistics for the periods 1969-2010 and 1970-2010, respectively. First, the data were cross-tabulated by days of the week and the available socio-demographic information (sex, age, religious affiliation and region). Second, time series of cumulated daily frequencies of suicide were analysed by seasonal Autoregressive Integrated Moving Average (ARIMA) models which included intervention effects accounting for Easter and Pentecost (Whit) holidays. First, the cross tabulations showed that weekly cycles may be smoothed above all in young persons and smoothed in drowning, jumping and car gas exhaustion suicides. Second, the ARIMA analyses displayed occasional preventive effects for holidays Saturdays and Sundays, and more systematic effects for holiday Mondays. There were no after effects on Tuesdays following holiday Mondays. In general, the weekend dip and the Monday backlog effect in suicide show striking similarities to the Advent season effect and are interpretable within the same template. The turning points between low and high frequencies possibly provide promising frames for the timing of prevention activities.