On intelligence and crime: A comparison of incarcerated sex offenders and serious non-sexual violent criminals

The impact of low IQ on crime has been a focus of debate for several decades now. Although sociologists have virtually removed it from the list of possible factors influencing crime, the impact of IQ on crime continues to generate a significant amount of scientific research and a substantial number of publications. The purpose of this study is to assess intellectual levels and to compare two groups of incarcerated criminals. Using MANCOVA and ANCOVA procedures, 261 sex offenders and 150 non-sexual violent criminals were compared on IQ subscales. The results show significant differences on vocabulary, comprehension, arithmetic, mental math computations, object assembly, letter-number sequencing, and perception subscales, as well as on performance IQ and total IQ. The impacts of penal filtering and sample composition are hypothesized to explain differences between the two subgroups. Theoretical and practical implications are discussed.