The definition and epidemiology of clusters of suicidal behavior: a systematic review.

Suicide clusters are a rare and underresearched phenomenon which attract wide media attention and result in heightened concern in the communities where they occur. We conducted a systematic literature review covering the definition and epidemiology of the time-space clustering of suicidal behavior. Of the 890 articles identified by electronic searching, 82 were selected for inclusion and the extracted data were analyzed by narrative synthesis. Less than a third of studies included a definition of a suicide cluster, and definitions varied considerably. Clusters occurred in various settings, including psychiatric hospitals, schools, prisons, indigenous communities, and among the general population. Most clusters involved young people. The proportion of all episodes that occurred in clusters varied considerably between studies and partly depended on study methodology (e.g., a larger proportion was found in studies of specific clusters compared with general population studies). Future studies should aim to combine the statistical analysis of time-space clustering with a case study of events, which examines potential links between individuals and the wider environmental context.