Changes in the seasonality of suicides over time in Slovenia, 1971 to 2002. Amplitude is only positively related to suicide rates among females

Background: Changes in the suicide rate within one region over time had been hypothesised to correspond to changes in suicide seasonality: a recent investigation from Italy confirmed such an assumption. Data from Slovenia were investigated to further evaluate the links between suicide rates and seasonal amplitude. Methods: A total of 14 325 male suicides and 4350 female suicides occurring in Slovenia from 1971 to 2002 were investigated with harmonic spectral analysis to extract their monthly seasonal dispersion by eight-year intervals. Changes in rate over time were analysed with a test for trend based on regression analysis. Results: The suicide rates of both males and females increased over time, with an evident peak in the 1987-1994 period and a decrease thereafter. Seasonality decreased across time in both sexes; however, no change of the peak was observed over time. The amplitude of the major 12-month cycle was slightly positively related to suicide rates, but the correlation was only statistically significant among females (P = 0.0053; males: P = 0.22). Limitations: Data could not be analysed according to age, the method of suicide, or the diagnosis attributable to the deceased, since this information was not available. Conclusion: The study confirmed that the seasonal effect on mortality by suicide is positively related to suicide rates, so much so that changes in suicide rates over time correspond to changes in suicide seasonality, but in Slovenia this effect was only evident among females, further pointing towards differences by sex in the mechanics leading to suicide. © 2007 Elsevier B.V. All rights reserved.