A prospective replication of the protective effects of IQ in subjects at high risk for juvenile delinquency.

The purpose of the study was to test the replicability of a protective effect of high IQ against criminality. Support has been found in prior studies for the hypotheses that Ss at high risk would have an elevated risk of serious criminal involvement, that seriously criminal Ss would have a lower mean IQ score than noncriminal Ss, and that Ss at high risk who had not become involved in serious criminal behavior would have the highest IQs. This report tests these hypotheses in a prospective design. Subjects were 1,037 members of a longitudinal investigation of a New Zealand birth cohort. IQs were examined for male and female Ss who were divided into 4 groups formed on the basis of risk status at age 5 years and delinquency outcome at ages 13 and 15. Analyses were conducted with and without mild delinquents excluded from the nondelinquent groups. We found that male and female delinquents showed significantly lower IQ scores than nondelinquents. By varying S selection procedures, we also found that a very high IQ may help boys, even those at risk, to stay free of delinquency altogether.