There is a well-established association between psychotic disorders and subsequent offending but the extent to which those who develop psychosis might have a prior history of offending is less clear. Little is known about whether the association between illness and offending exists in non-psychotic disorders. The aim of this study was to determine whether the association between mental disorder and offending is present prior to illness onset in psychotic and non-psychotic disorders.
In a nested case-control study, cases (n=101,890) with a first psychiatric contact during the period 1995 to 2006 were identified and matched by age and gender to population-based controls (n=2,236,195). Exposure was defined as prior criminal and violent offending.
Males with one offence had an incidence rate ratio (IRR) of 2.32 [95% confidence interval (CI) 2.26-2.40] for psychiatric admission whereas two or more convictions yielded an IRR of 4.97 (95% CI 4.83-5.11). For violent offending the associations were stronger and IRRs of 3.97 (95% CI 3.81-4.12) and 6.18 (95% CI 5.85-6.52) were found for one and several offences respectively. Estimates for females were of a similar magnitude. The pattern was consistent across most diagnostic subgroups, although some variability in effect sizes was seen, and persisted after adjustment for substance misuse and socio-economic status (SES).
A prior history of offending is present in almost one in five patients presenting to mental health services, which makes it an important issue for clinicians to consider when assessing current and future risks and vulnerabilities.