Childhood family income, adolescent violent criminality and substance misuse: quasi-experimental total population study.

BACKGROUND: Low socioeconomic status in childhood is a well-known predictor of subsequent criminal and substance misuse behaviours but the causal mechanisms are questioned. Aims To investigate whether childhood family income predicts subsequent violent criminality and substance misuse and whether the associations are in turn explained by unobserved familial risk factors. 

METHOD: Nationwide Swedish quasi-experimental, family-based study following cohorts born 1989-1993 (n(total) = 526 167, n(cousins) = 262 267, n(siblings) = 216 424) between the ages of 15 and 21 years. 

RESULTS: Children of parents in the lowest income quintile experienced a seven-fold increased hazard rate (HR) of being convicted of violent criminality compared with peers in the highest quintile (HR = 6.78, 95% CI 6.23-7.38). This association was entirely accounted for by unobserved familial risk factors (HR = 0.95, 95% CI 0.44-2.03). Similar pattern of effects was found for substance misuse. 

CONCLUSIONS: There were no associations between childhood family income and subsequent violent criminality and substance misuse once we had adjusted for unobserved familial risk factors.