Researchers collected data on all 959 patients discharged from medium secure units in England and Wales between 1997 and 1998 and used the offenders' index to find details of subsequent convictions.
In the two years after discharge, only 6% of psychiatric patients committed a violence offence. The strongest association with offending was previous offending.
Substance misuse and sexual abuse were associated with increased offending risk, although patients were less likely to be convicted after a lengthy admission or if they had a history of self harm. Aftercare is also effective in preventing reconviction.
The rate of violent offending is so low that there is little scope for overall reduction and it would be better concentrate on the identification of high risk patients, say the authors.
One American study identified a psychopathy "checklist" as the best single predictor of violence in psychiatric patients, and the authors recommend further exploration of its use in medium security hospitals in England and Wales.