IQ and violent criminal behavior

Hmm. A little confusing. From Is the Association between General Cognitive Ability and Violent Crime Caused by Family-Level Confounders? by Thomas Frisell, Yudi Pawitan, Niklas Långström. From the Abstract:

Background

Research has consistently found lower cognitive ability to be related to increased risk for violent and other antisocial behaviour. Since this association has remained when adjusting for childhood socioeconomic position, ethnicity, and parental characteristics, it is often assumed to be causal, potentially mediated through school adjustment problems and conduct disorder. Socioeconomic differences are notoriously difficult to quantify, however, and it is possible that the association between intelligence and delinquency suffer substantial residual confounding.

Methods

We linked longitudinal Swedish total population registers to study the association of general cognitive ability (intelligence) at age 18 (the Conscript Register, 1980–1993) with the incidence proportion of violent criminal convictions (the Crime Register, 1973–2009), among all men born in Sweden 1961–1975 (N = 700,514). Using probit regression, we controlled for measured childhood socioeconomic variables, and further employed sibling comparisons (family pedigree data from the Multi-Generation Register) to adjust for shared familial characteristics.

Results

Cognitive ability in early adulthood was inversely associated to having been convicted of a violent crime (β = −0.19, 95% CI: −0.19; −0.18), the association remained when adjusting for childhood socioeconomic factors (β = −0.18, 95% CI: −0.18; −0.17). The association was somewhat lower within half-brothers raised apart (β = −0.16, 95% CI: −0.18; −0.14), within half-brothers raised together (β = −0.13, 95% CI: (−0.15; −0.11), and lower still in full-brother pairs (β = −0.10, 95% CI: −0.11; −0.09). The attenuation among half-brothers raised together and full brothers was too strong to be attributed solely to attenuation from measurement error.

Discussion

Our results suggest that the association between general cognitive ability and violent criminality is confounded partly by factors shared by brothers. However, most of the association remains even after adjusting for such factors.

My interpretation. We have long had good theoretical grounds to believe that lower cognitive capability is causally related to higher risk for violent and other antisocial behavior.

However, it is methodologically difficult to measure some of the issues (socioeconomic status, parental characteristics, ethnicity, etc.) which could confound and weaken the relationship between low cognitive ability and high violence and other antisocial behavior.

This team found some other approaches to test whether the other confounding factors might be more important than cognitive ability. The confounds have little explanatory value. They seem to have confirmed the causal role of low cognitive ability on higher violence and antisocial behavior.

I believe that low cog deficits can be off-set, at least to an extent, by strong cultural norms, good behavioral choices, personality dispositions, and other such factors. But this shores up the proposition that low cog has a range of likely negative consequences. Knowing low cog, interventions need to come early and on the range of other factors which might be militating.