IQ, SES, and criminality

(Via Chuck.) Elaboration on the association between IQ and parental SES with subsequent crime. Personality and Individual Differences 50 (2011) 1233–1237. (pdf)

The current study, based on the nationally representative NLSY data, follows incarceration over a 24-year period. This represents the longest prospective examination of the NLSY crime data to date, since previous analyses have been shorter and is not prospective (Herrnstein & Murray, 1994). With the aim of providing greater confidence in the results, unlike prior analyses the current study uses three major criminological outcomes (onset, incidence and frequency of incarceration), and not one (incidence of incarceration). Based on theoretically reformulated associations between the study variables, the results show that low IQ, low parental SES and their interaction modestly predict the incidence of, frequency of and time to incarceration.

Theoretically, a low IQ may make coping and decision-making difficult and increase the likelihood of crime. Taken in isolation the association between low IQ and increased risk of crime in the current results may be taken as evidence that is consistent with the Bell Curve (Herrnstein & Murray, 1994). Concurrently, however, the present results also indicate that a low parental SES increases the risk of crime, potentially through an inadequate familial environment (Bradley & Corwyn, 2002). These family characteristics may include little emphasis on social attainment. Thus, the current findings indicate that the family environment may provide a route to influence the association between IQ and crime. This possibility is not considered in the Bell Curve view on crime that emphasizes neighborhood SES (Herrnstein & Murray, 1994), and is consistent with opponents to the Bell Curve (Fischer et al., 1996).

Collectively, however, the effects of IQ and parental SES on crime are modestly amplified, as captured by the interaction reflecting unfavorable conditions (i.e., particularly if both IQ and parental SES are low). A possible explanation of this interaction is that a disadvantaged home environment does not encourage social attainment and a low IQ makes coping and decision-making difficult. Taken together this increases the likelihood of crime. Thus these findings support an interactional perspective of crime. Their interpretation is consistent with the usually competing theoretical notions that contrast low SES (Fischer et al., 1996) or low IQ (Herrnstein & Murray, 1994) as factors that increase the likelihood of crime. [. . .]

This study does not separate genetic–environmental influences, unlike past research (e.g., Koenen, Caspi, Moffitt, Rijsdijk, & Taylor, 2006). SES may not purely be an environmental factor that is unrelated to IQ. Parents may give children both genes for IQ and SES (i.e., passive gene–environment associations), and a parent’s SES is partly based on their IQ as a result of life-long active gene–environment interactions. Accordingly, IQ and SES may be moderately correlated due to common genetic influences. Also, as the participants in this study mature, they become increasingly free to create their own environments, partly due to both IQ and SES. The current study, however, affords no assessment of genetics, or upward or downward social mobility, thereby highlighting key directions for future research.

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