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Empirical studies using the PCL-R (Hare, 2003) have shown no intelligence differences between psychopaths and nonpsychopaths. However, Cleckley (1976) argued that psychopaths often show superior intelligence. The purpose of the present study was to test the hypothesis that the correlation between intelligence and severity of criminal development is the opposite in psychopaths than in nonpsychopathic criminals using a sample of 370 men sentenced for violent (nonsexual) crimes. That pattern would provide a way of explaining the discrepancy between Cleckley's view and later empirical work. The results showed that for nonpsychopaths, higher total IQ and particularly verbal intelligence meant a later start in violent crime. For those diagnosed as psychopaths, however, this association was reversed.
What role does intelligence play in criminality? According to research, it seems to have a preventive effect. Intelligence, as measured by IQ tests, is negatively correlated with criminality (Hirschi & Hindelang, 1977), and this association seems to appear in early childhood (Stattin & Klackenberg-Larsson, 1993), among early teenage boys (Lynam, Moffit, SL Stouthamer-Loeber, 1993), and among adult criminals (Vaillant, Asu, Cooper, & Mammola, 1984; Yeudall & Wardell, 1978; Yeudall, Fedora, Fedora, & Wardell, 1981). On average, delinquents score eight IQ points lower than nondelinquents on standard intelligence tests (Lynam et al., 1993), and the relation between intelligence and criminality is stronger for violent than nonviolent offenders (DeWolfe & Ryan, 1984; Heilbrun, 1982; Heilbrun & Heilbrun, 1985; Holland & Holt, 1975; Holland, Beckett, & Levi, 1981). The existence of this negative relation is one of the most robust findings across numerous studies of juvenile delinquency. In fact, all previous reviews of the literature on IQ and delinquency have concluded that a negative relation exists (Caplan, 1965; Hirschi & Hinderlang, 1977; Wilson & Herrnstein, 1985; Woodward, 1955). Thus, the robust findings from research are that criminals tend to be less intelligent than noncriminals, particularly concerning verbal abilities, and that violent criminals are likely to be less intelligent than other criminals.
If violent criminals are less intelligent, on average, than nonviolent criminals, then one would expect criminal psychopaths, who tend to be particularly violent, to be particularly low in intelligence. Psychopaths are defined by personality features such as remorsnessness, callousness, deceitfulness, egocentricity, failure to form close emotional bonds, low anxiety, superficial charm, and...