The relationship between daylight hours and suicides seasonality in Russia

Researchers from various countries across the globe have found suicidal behaviour to exhibit seasonality. In Russia and other countries located in the northern hemisphere it is observed that the number of suicides spikes during the spring to summer period and drops in winter. Researching the seasonal fluctuations of suicide mortality will allow us to better understand this phenomenon and, consequently, to develop effective measures of suicide prophylaxis, which help prevent future suicide cases. In this article we research whether the seasonality of suicide levels in Russian countries is related to the daylight hours in different months. To achieve this, seasonality indices for suicides and daylight hours have been constructed for 8 Russian cities located across different latitudes. For these indices Pearsons correlation coefficient has been computed. Granger causality test has been performed for the Russian suicide mortality data obtained for the years from 2000 to 2021. The authors have also attempted to estimate the real number of suicides by including some other causes of death, which were classified as events of undetermined intent. The results of the study show significant high positive correlation between the seasonality indices of suicides and daylight hours (ranging between 0.74 and 0.9 depending on the city) as well as the presence of Granger causality for all researched cities when using 2 and 3 lags, which might imply a potential influence of the daylight hours on the suicidal behaviour in Russia. This research contributes to academic literature on the seasonal patterns in suicides and their potential causes.