Academic Achievement as a Potential Confound
The association between intelligence and antisociality is confounded-largely because those with lower intelligence are likely to do less well in school. School is very important in the life of children as we touched upon in Chapter 2, and school failure is associated with many adverse psychological and social outcomes. Only one study controlled for academic achievement (grades), specifically, which, as we will see in Chapter 5 is perhaps the most important school-related control variable. Two studies report robust associations, controlling for other school factors. Piquero (2000) controlled for school discipline problems and still found that WISC scores were associated with violence. Bellair and McNulty (2010) used data from the National Longitudinal Survey of Youth and controlled for high school drop-out and still found a significant association between cognitive skills and violence. Findings by Chen et al. could also be said to be mildly supportive. In 3 out of 4 comparisons reported, violent offenders had lower scores on cognitive control than nonviolent offenders matched on education (Chen, Muggleton, Juan, Tzeng, & Hung, 2008).
In other cases, the estimated associations between intellectual ability and violence were in the right direction, but not strong when authors controlled for a variety of school factors (e.g., Bauer, 2000; Cohen et al., 2003). Bellair and McNulty (2005) found that the Peabody test of verbal ability was no longer significantly associated with violence in their multivariate analysis, which did include a control for school grades, but they added many variables to the model, including violence in a prior wave of data, so it is likely that this estimate is overly conservative. Thus, we cannot ascertain with existing studies whether the association between intellectual ability and violence is robust with respect to academic achievement and other school factors. Future studies accounting for academic achievement as a control variable and also testing whether IQ has an indirect on violence via its influence on academic achievement would be needed to feel confidence in our conclusions about the association between IQ, executive functioning and violence.