Contribution of imitative suicide to the suicide rate in prisons.

Suicide rates in prisons are high. Our aim was to investigate the contribution of imitative suicide to the prison suicide rate. We used Knox tests for space-time clustering in a case register of natural and self-inflicted deaths in prisons in England and Wales and model simulations to estimate the effect size. We found significant space-time clustering among 657 self-inflicted deaths in 90 prisons over 10 years but no space-time clustering among 430 deaths from natural causes in 87 prisons over this period. Model simulations with an imitation rate of 5.8% (CI 1%-11%) reproduced the observed space-time clustering.