Criminal offending and the family environment: Swedish national high-risk home-reared and adopted-away co-sibling control study.

BACKGROUND: Criminal offending is strongly transmitted across generations.

AIMS: To clarify the contribution of rearing environment to cross-generational transmission of crime.

METHOD: Using Swedish national registries, we identified 1176 full-sibling and 3085 half-sibling sets from high-risk families where at least one sibling was adopted and the other raised by the biological parents.

RESULTS: Risk for criminal conviction was substantially lower in the full- and half-siblings who were adopted v. home-reared (hazard ratios (HR) = 0.56, 95% CI 0.50-0.64 and 0.60, 95% CI 0.56-0.65, respectively). The protective effect of adoption was significantly stronger in sibships with two v. one high-risk parent.

CONCLUSIONS: Using matched high-risk full- and half-siblings, we found replicated evidence that (a) rearing environment has a strong impact on risk for criminal conviction, (b) high-quality rearing environments have especially strong effects in those at high familial risk for criminal offending and (c) the protective effects of adoption are stronger for more severe crimes and for repeated offending.