Intelligence and Crime

Once the IQ-crime correlation is measured, the next task is to explain it. Why are IQ and crime negatively correlated? Explanations of the IQ-crime correlation typically take one of three approaches, that: (1) IQ and crime are spuriously, not causally, correlated; (2) low IQ increases criminal behavior; or (3) criminal behavior decreases IQ.

A popular argument against IQ as a cause of crime criticizes IQ tests as only measuring middle-class knowledge and values rather than innate intelligence. As a result, the observation that some minority groups and the poor score low on IQ tests simply reflects their diverse cultural backgrounds. These same groups also commit proportionately more crime because they suffer structural disadvantages such as poverty and discrimination. Consequently, the same people who score low on IQ tests also tend to commit more crime, and so IQ and crime are empirically correlated, thus this correlation is not causal but reflects only culturally biased testing of intelligence.

A variation of this argument holds that the structural disadvantages that increase crime rates also reduce educational opportunities thus lessening individuals' ability and motivation to score well on IQ tests. The IQ-crime correlation occurs only because they are both rooted in structural disadvantage, which, in statistical terms, represents a "spurious" correlation.

Although these discrimination hypotheses have wide appeal, they have received fairly little support in empirical studies, for IQ and crime are significantly correlated within race and class groups as well as when statistically controlling for race, class, test-taking ability, and test-taking motivation (e.g., Hirschi and Hindelang; Lynam et al.).

Another argument against IQ as a cause of crime holds that school teachers and administrators treat students differently by perceptions of the students' intelligence—giving negative labels and fewer educational opportunities to less intelligent students. These labels and constrained opportunities, in turn, produce feelings of alienation and resentment that lead students to delinquent peers and criminal behavior (Menard and Morse). As such, society's reaction to intelligence, and not any property of intelligence itself, increases criminal behavior. Unfortunately, few studies have adequately tested this labeling hypothesis.

A final argument against IQ holds that even if all people commit crime with equal frequency, less intelligent people would be less able to evade detection and would be arrested more often. This detection hypothesis has received some empirical support in that IQ scores tend to correlate more strongly with officially recorded crime than self-reported crime. However, most studies still find a significant correlation between IQ and self-reported crime, which is not easily explained by differential police detection (e.g., Moffitt and Silva).

In contrast to the above spurious arguments, some explanations emphasize IQ as a cause of crime. The earliest causal explanation, popular during the early 1900s, portrayed criminals as so "feebleminded" and "mentally deficient" that they could neither distinguish right from wrong nor resist criminal impulses. This feeblemindedness hypothesis, however, lost favor long ago as it became clear that few criminals are actually mentally deficient and most recognize, though may not follow, behavioral norms (Moffitt et al.).

A more recent, and more compelling, causal explanation emphasizes the importance of intelligence—especially verbal intelligence—during childhood socialization. The socialization of children involves constant verbal communication and comprehension of abstract symbols; therefore, children with poor verbal and cognitive skills have greater difficulty completing the socialization process, which puts them at risk of undercontrolled, antisocial behavior. Empirical studies overall have supported this developmental hypothesis (Moffitt, p. 116), and it fits with the especially strong correlation between verbal IQ and crime.

A final causal explanation links IQ to crime through school performance. Less intelligent students do less well in school, which results in academic frustration. This frustration, in turn, weakens their attachment and commitment to schooling, and a weakened bond to school, as per social control theory, allows for more criminal behavior (Hirschi and Hindelang). This school-performance hypothesis has received strong support from empirical studies, and it is probably the most widely accepted explanation of the IQ-crime correlation (Moffitt).

One last approach to IQ and crime deserves mention even though few criminological studies have examined it. Rather than low IQ increasing criminal behavior, criminal behavior might decrease IQ. Many facets of a criminal lifestyle can impair cognitive abilities, including physical injuries, especially head traumas, drug use, and withdrawing from school (Moffitt).