NEW YORK (Reuters Health) — Men convicted of rape or other sexual offences have a much higher-than-average rate of serious mental illness and history of psychiatric hospitalisation, a new study suggests.The findings, published in the Journal of Clinical Psychiatry, run counter to conventional wisdom. Experts have traditionally held the view that the mentally ill are not more likely to be sexual offenders.

However, part of this belief may stem from comparisons with people convicted of murder, who appear to have a higher rate of psychiatric disorders than sex offenders do.

The new study, in contrast, compared male sexual offenders with men in the general population. It found that offenders were six times more likely to have ever been hospitalised for a mental illness.

This raises the possibility that identifying and treating these disorders could lower the odds of offenders repeating their crimes, said lead study author Dr. Seena Fazel of Oxford University in the UK.

“The criminal justice system needs to be aware that people who shows signs of being unwell need to be assessed,” he told Reuters Health.

Fazel and his colleagues based their findings on data from Sweden’s system of population registers, which includes databases on criminal convictions and hospitalisations for psychiatric illness.

The researchers compared 8,495 men convicted of sexual offences between 1988 and 2000 with a sample of 19,935 men from the general population.

Sex offenders were five times more likely to have been hospitalised for schizophrenia or other psychotic disorders, and were three times more likely to have a history of bipolar disorder.

They also had a four-fold greater risk of alcohol or drug dependence, and were 30 times more likely to have been diagnosed with a personality disorder.

In all, 24 percent of sexual offenders had a history of psychiatric hospitalisation, versus less than five percent of men in the general population.