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.