Faculty of Political Science and Economics, Waseda University, Building No. 3, 1-6-1 Nishiwaseda, Shinjuku-ku, Tokyo 169-8050, Japan. Electronic address: mueda@waseda.jp.
BACKGROUND: Previous research on hourly diurnal variation in suicide frequency has often suffered from geographical and time-span limitations in the data. We studied diurnal and daily variations of suicide by analyzing a large dataset based on the national death registry in Japan between 1974 and 2014.
METHODS: The diurnal and daily patterns of 873,268 suicide deaths over 41 years were examined by sex and age group through Poisson regression and visual inspection. We also investigated whether these patterns are related to Japan's economic conditions.
RESULTS: Suicide by middle-aged males was most frequent in the early morning especially on Mondays after the end of Japan's high growth period. We also observed large midnight peaks in suicides among young and middle-aged males. The proportion of early morning suicide deaths by young and middle-aged males increased as the country's unemployment rose. Females and elderly males were more likely to die by suicide during the day than at night. LIMITATION: Our study examined time of death, not time of suicide attempt. It is possible that there is a discrepancy between the two.
CONCLUSIONS: Different subpopulations die by suicide at different times of the day and days of the week. Time patterns of suicide varied considerably over time, suggesting that they cannot be explained by biological circadian rhythm alone. Our findings suggest that the patterns are partly explained by economic conditions. Future suicide prevention efforts should consider the time patterns of suicide unique to each subpopulation, especially when economic growth is depressed.