Clustering of suicides among people with mental illness

BACKGROUND: Most previous investigations of imitative suicide have reported suicide clustering in the general population, either temporal clustering following media reporting of suicide or case studies of geographically localised clusters. AIMS: To determine whether space - time and space-time-method clustering occur in a national case register of those who had recent contact with mental health services and had died by suicide and to estimate the suicide imitation rate in this population. METHOD: Knox tests were used for space-time and space-time-method clustering. Model simulations were used to estimate effect size. RESULTS: Highly significant space-time and space-time-method clustering was found in a sample of 2741 people who died by suicide over 4 years who had had recent contact with one of 105 mental health trusts. Model simulations with an imitation rate of 10.1% (CI 4-17) reproduced the observed space-time-method clustering. CONCLUSIONS: This study provides indirect evidence that imitative suicide occurs among people with mental illnesses and may account for about 10% of suicides by current and recent patients.