Background: Conduct disorder (CD) prior to age 15 has been associated with an increased risk of aggressive behaviour and crime among men with schizophrenia. The present study aimed to replicate and extend this finding in a clinical sample of severely mentally ill men and women.
Method: We examined a cohort of in-patients with severe mental illness in one mental health trust. A total of 205 men and women participated, average age 38.5 years. CD was diagnosed using a structured diagnostic tool. Alcohol and illicit drug use, aggressive behaviour and victimization were self-reported. Information on convictions was extracted from official criminal records. Analyses controlled for age and sex.
Results: CD prior to age 15 was associated with an increased risk of assault over the lifespan [odds ratio (OR) 3.98, 95% confidence interval (CI) 1.87-8.44)], aggressive behaviour in the 6 months prior to interview (OR 2.66, 95% CI 1.24-5.68), and convictions for violent crimes (OR 3.19, 95% CI 1.46-6.97) after controlling for alcohol and illicit drug use. The number of CD symptoms present prior to age 15 significantly increased the risk of serious assaults over the lifespan, aggressive behaviour in the past 6 months, and violent crime after controlling for alcohol and illicit drug use.
Conclusions: Men and women with severe mental illness who have a history of CD by mid-adolescence are at increased risk for aggressive behaviour and violent crime. These patients are easily identifiable and may benefit from learning-based treatments aimed at reducing antisocial behaviour. Longitudinal, prospective investigations are needed to understand why CD is more common among people with than without schizophrenia.