Inhibition deficits of serious delinquent boys of low intelligence

Introduction: Studies have shown that low intelligence (IQ) and delinquency are strongly associated. This study focuses on inhibitory deficits as the source for the association between low IQ and delinquency. Further, the authors explore whether serious delinquent boys with a low IQ are exposed to more risk factors than serious delinquent boys with an average to high IQ. They also examine the extent to which low IQ and higher IQ serious delinquents incurred contact with the juvenile court because of their delinquent behaviour. Methods: Cross-sectional and longitudinal data from the Pittsburgh Youth Study were used to constitute four groups of boys: low IQ serious delinquents (n = 39), higher IQ serious delinquents (n = 149), low IQ non-to-moderate delinquents (n = 21) and higher IQ non-to-moderate delinquents (n = 219). Results: Low IQ serious delinquents committed more delinquent acts than higher IQ serious offenders. Low IQ serious delinquent boys also exhibited the highest levels of cognitive and behavioural impulsivity. There were no differences between low IQ and higher IQ serious delinquents on measures of empathy and guilt feelings. Instead, elevations on these characteristics were associated with serious offenders as a whole. Compared with higher IQ serious delinquents, low IQ serious delinquents were exposed to more risk factors, such as low academic achievement, being old for grade, depressed mood and poor housing. Conclusions: Inhibition deficits appear important in the aetiology of delinquency, especially among low IQ boys. Serious delinquent boys are all impulsive, but the higher IQ serious delinquents seem to have a better cognitive control system. Interventions aimed at low IQ boys should focus on the remediation of behavioural impulsivity as well as cognitive impulsivity.