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

https://doi.org/10.1016/j.ijlp.2004.03.010Get rights and content

Abstract

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.

Section snippets

Intelligence and crime

Over the last few decades, much evidence has suggested that intellectual functioning is associated with crime (Hirschi & Hindelang, 1977, Wilson & Herrnstein, 1985). While many researchers consider sociological factors, such as ethnicity or poverty, to be largely responsible for crime, others have attempted to demonstrate the importance of intellectual functioning in the understanding of criminal behavior. There have been two main explanations of the role of intellectual performance in crime.

Intelligence and violent crimes

In an attempt to understand the relationship between IQ and delinquency, Spellacy, 1977, Spellacy, 1978 studied Wechsler IQ scores for incarcerated offenders. Non-violent subjects, comparable in terms of age, race, and laterality, were compared with violent offenders. Violent offenders showed lower scores, with differences ranging from 10.3 points to 13.8 points, compared with non-violent offenders. Similar results were observed by Holland and his colleagues (Holland et al., 1981, Holland &

Intelligence and crime in sex offenders

Among studies of intellectual performance, a wide range of studies have discussed the impact of intellectual functioning on either the criminal career or the modus operandi of sex offenders. Only a few studies have attempted to empirically investigate the question (Okami & Goldberg, 1992). Much of the research on sex offenders has addressed the question of the specificity of sex offenders by comparing sex offenders with traditional criminals. Most studies did not find significant differences

Subjects

The subjects in this study consisted of a sample of 411 offenders incarcerated at the Regional Reception Centre (RRC), a maximum-security facility of Correctional Services of Canada. The sample was comprised of offenders from the Province of Québec sentenced to two or more years of incarceration, who are all channeled through the RRC. The subjects' treatment needs and correctional risk levels were evaluated during a 4- to 6-week procedure. Of the 411 offenders, 261 were sex offenders and 150

Results

The aim of this study was to compare sex offenders with NSV offenders on IQ results, namely, on all eleven scales, as well as on three composite indexes. To test for significant differences between the eleven intelligence subscales and the independent fixed factor of criminal subtype, a multivariate analysis of covariance (MANCOVA) was performed. In order to control for the possible confounding effects of other relevant variables, covariates were used to statistically control for the subjects'

Discussion

The results from the current study indicate that sex offenders differ from non-sexual violent criminals in terms of IQ. Differences between sex offenders and NSV criminals are particularly significant on total and performance IQ scores. When compared with NSV criminals, sex offenders showed significantly lower results on performance scales. While research on NSV criminals tends to show mental imbalance (higher performance on non-verbal than on verbal IQ), sex offenders tend to perform poorly on

Limitations of the study

The current study is clearly not without its limitations. First, while the sample chosen was adequate to allow us to compare NSV criminals with sex offenders, it was not representative of all sexual criminals. The sex offenders and NSV criminals were selected from a population of serious offenders sentenced to two or more years of incarceration. The two main factors affecting decision making throughout the criminal justice system (from the arrest decision to the release decision) are the

Acknowledgements

This research was supported by a doctoral grant provided by the Social Sciences and Humanities Research Council of Canada (SSHRC). The authors wish to thank Serge Larivée for his substantive and stylistic editing. Special thanks are also due to Michel St-Yves and Tony Brien for their meticulous data collection.

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