SECTION 2 The Differential Etiology of Violence Developmental Factors
Intelligence, Executive Function, and Violence
In this chapter, we hypothesize that intelligence and intellectual deficits have a special relationship with violence, and we examine the existing literature to see if this view is supported. We presented background reasoning for this proposition in Chapter 2. Here, we will provide a review of the literature, followed by the methodology used to identify studies for our evaluation, and comprehensive review of those studies.
INTELLIGENCE AND VIOLENCE
Intelligence deficits have been associated with violent behavior in adolescents and adults in many studies (e.g., Ayduk et al., 2007; Barker et al., 2007; Cohen et al., 2003; Giancola, 2000b; Holland, Beckett, & Levi, 1981). Holland et al. (1981) show that violent offenders have significantly lower IQ than nonviolent ones, with recidivistic violent offenders having the lowest IQ of all. Striking differences in cognitive ability have been reported between violent and nonviolent offenders (Barker et al., 2007), and IQ has also been negatively associated with psychopathy (Burke, Loeber, & Lahey, 2007).
Authors of most studies do not employ adequate controls to ensure that the relationships between intelligence and violence are causal. Menard and Morse (1984) made the case that low IQ was spuriously related to delinquency due to their common association with low academic performance and consequent negative labeling, reduced academic access, and school alienation. As of this writing, this argument has not been fully adjudicated (see also Harry & Minor, 1986). Ward and Tittle (1994) did find that IQ had an indirect effect on delinquency via its effect on school performance and school attitudes, and the direct effect of IQ on general delinquency was no longer statistically significant in the path model.
There are several reasons that indicators of intelligence, verbal ability, and executive functioning might be associated with violent behavior, beyond their influence on general delinquency and we discussed these at some length in Chapter 2. In the following sections, we first review the status of findings about associations between intellectual ability and violence, and then we report our own systematic review designed to enhance our understanding of the differential etiology of violence.