Time variations in injury incidence.

Study objective: to present time variations in the incidence of injuries on a community level.

Population and methods: all injuries which occurred in a defined population of the municipality of Harstad were registered prospectively from 1 January 1986 to 31 December 1991. Variations over time in monthly incidence of seven types of injuries (home, traffic, street, sports, work, other, unknown) were analysed by the Autoregressive Integrated Moving Average Analysis (ARIMA).

Results: a total of 9,685 injuries was registered during the six year follow-up period. No significant secular trend was observed for any of the analysed types of injuries. Series of monthly incidence of traffic, street, and sports injuries showed seasonal-dependent variations. Incidence of traffic injuries was highest during the summer months, while incidence of sports and street injuries was highest during the winter months.

Conclusions: both the existence of seasonal dependency in injury incidence and the relatively high random variations in monthly injury incidence imply that evaluation of community based injury control programmes should include incidence during at least a one year period before the intervention has started.