Suicides in California (1968-1977): absence of seasonality in Los Angeles and Sacramento counties.

Since the turn of the century, there have been numerous publications on the seasonality of suicide. Rarely has the duration of sunlight exposure or any other weather parameter been quantitated in studies of suicide seasonality. To explore the relationships between sunlight and suicide, we examined California weather and suicide data from 1968 to 1977. Los Angeles County and Sacramento County were well-suited to the investigation, as complete data were available for these large population centers. There was no evidence of seasonality to suicides in L.A. County or Sacramento, despite a pronounced seasonality to weather. To investigate the acute temporal effects of weather on suicides, all occurrences of 10 successive above- or below-average sunshine days were identified. Suicides of for intervals of 5 days were then compared by Mann-Whitney analyses for 25 days after the selected intervals. For L.A. County, there were no significant findings. For Sacramento County, however, there was evidence for sunlight inhibition of suicides at days 21-25 after the above-average sunshine. Suicides after 10 days of below-average sunshine were increased as much as 70% about the 10-year average. Further replication studies with larger data sets are needed for an adequate examination of the correspondences of suicide data and weather measurements.