Abstract
We aimed to investigate the heterogeneity of seasonal suicide patterns among multiple geographically, demographically and socioeconomically diverse populations. Weekly time-series data of suicide counts for 354 communities in 12 countries during 1986-2016 were analysed. Two-stage analysis was performed. In the first stage, a generalised linear model, including cyclic splines, was used to estimate seasonal patterns of suicide for each community. In the second stage, the community-specific seasonal patterns were combined for each country using meta-regression. In addition, the community-specific seasonal patterns were regressed onto community-level socioeconomic, demographic and environmental indicators using meta-regression. We observed seasonal patterns in suicide, with the counts peaking in spring and declining to a trough in winter in most of the countries. However, the shape of seasonal patterns varied among countries from bimodal to unimodal seasonality. The amplitude of seasonal patterns (i.e. the peak/trough relative risk) also varied from 1.47 (95% confidence interval [CI]: 1.33-1.62) to 1.05 (95% CI: 1.01-1.1) among 12 countries. The subgroup difference in the seasonal pattern also varied over countries. In some countries, larger amplitude was shown for females and for the elderly population (≥65 years of age) than for males and for younger people, respectively. The subperiod difference also varied; some countries showed increasing seasonality while others showed a decrease or little change. Finally, the amplitude was larger for communities with colder climates, higher proportions of elderly people and lower unemployment rates (p-values < 0.05). Despite the common features of a spring peak and a winter trough, seasonal suicide patterns were largely heterogeneous in shape, amplitude, subgroup differences and temporal changes among different populations, as influenced by climate, demographic and socioeconomic conditions. Our findings may help elucidate the underlying mechanisms of seasonal suicide patterns and aid in improving the design of population-specific suicide prevention programmes based on these patterns.
Highlights
IntroductionAbundant research dating back to the 19th century demonstrates seasonal suicide patterns, with an increase in spring and a decrease in winter (Durkheim, 1897; Maes et al, 1993; Chew and McCleary, 1995; Ajdacic-Gross et al, 2010; Christodoulou et al, 2012; Woo et al, 2012; Roehner, 2015; Dixon and Kalkstein, 2018; Yang et al, 2019)
They indicate that there exist strong seasonal patterns of suicide in most of the countries, while the patterns were heterogeneous among the countries
We confirmed that the spring peak in suicide numbers was consistently observed in almost all countries, but the shape and amplitude of seasonality, subgroup difference and temporal changes varied between countries
Summary
Abundant research dating back to the 19th century demonstrates seasonal suicide patterns, with an increase in spring and a decrease in winter (Durkheim, 1897; Maes et al, 1993; Chew and McCleary, 1995; Ajdacic-Gross et al, 2010; Christodoulou et al, 2012; Woo et al, 2012; Roehner, 2015; Dixon and Kalkstein, 2018; Yang et al, 2019). Almost all previous studies on seasonal suicides investigated a study population that was relatively homogeneous (e.g. a single city, a single country or a few communities within a country) (Woo et al, 2012). These studies differed in terms of experimental design and statistical methodology, making it difficult to directly compare results or quantify heterogeneity among different populations (Woo et al, 2012)
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