Treatmentof Research andSexual Abuse: A Journal - XX(X) 1 –29 - 8 April 2013

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Typically, neuropsychological studies of sex offenders have grouped together different types of individuals and different types of measures. This is why results have tended to be nonspecific and divergent across studies. Against this background, the authors undertook a review of the literature regarding the neuropsychology of sex offenders, taking into account subgroups based on criminological theories. They also conducted a meta-analysis of the data to demonstrate the cognitive heterogeneity of sex offenders statistically. 

Their main objective was to test the hypothesis to the effect that the neuropsychological deficits of sex offenders are not broad and generalized compared with specific subgroups of participants based on specific measures. In all, 23 neuropsychological studies reporting data on 1,756 participants were taken into consideration. 

As expected, a highly significant, broad, and heterogeneous overall effect size was found. Taking subgroups of participants and specific cognitive measures into account significantly improved homogeneity. 

  • Sex offenders against children tended to obtain lower scores than did sex offenders against adults on higher order executive functions, whereas 
  • sex offenders against adults tended to obtain results similar to those of non-sex offenders, with lower scores in verbal fluency and inhibition. 

However, it is concluded that neuropsychological data on sex offenders are still too scarce to confirm these trends or to test more precise hypotheses. For greater clinical relevance, future neuropsychological studies should consider specific subgroups of participants and measures to verify the presence of different cognitive profiles.

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The first objective of this study was to conduct a comprehensive review of the literature regarding the neuropsychology of sex offenders. Though the number of studies found was impressive (k = 113, references with one asterisk in the reference list), nearly half focused exclusively on IQ and only 23 presented results on individual neuropsychological tests and used a comparison group. 

It could be concluded that the number of neuropsychological studies based on validated tasks and experimental designs (with subgroups) is still very low in the field of sexual deviance.

Our second objective was to demonstrate empirically that sex offenders represent a heterogeneous group from a neurocognitive point of view. As expected, the Q-tests of heterogeneity of effect sizes were highly significant for sex offenders. This suggests that it is preferable to avoid regrouping different types of sexual offenders and/or measures in neuropsychological studies (e.g., .... ). 

In this study, homogeneity improved when subgroups were considered separately. 

  • On one hand, homogeneity might have improved simply as a result of repeatedly fragmenting the sample into smaller groups (... ...). 
  • On the other hand, other key moderating factors still present might have influenced the heterogeneity of results. 

These include 

  • preferential versus situational types of sex offenders against children and 
  • exclusive versus nonexclusive types of pedophiles (Holmes & Holmes, 2009). 

As the available data were too few for these moderators to be included in the study, future neuropsychological assessments focusing on more refined subgroups of sex offenders should help resolve this question.

Our main goal was to determine whether different subgroups of sex offenders showed different cognitive profiles when individual neuropsychological tasks are used. Unfortunately, only two broad subgroups of sex offenders and a few traditional neuropsychological tests could be included in the meta-analysis. 

It is clear from the analyses that sex offenders as a group present significant and wide-ranging cognitive impairments compared with the general population. Interestingly, however, somewhat different cognitive performances were observed when sex offenders against children, sex offenders against adults, and non-sex offenders were considered separately. 

First, sex offenders against children tended to score lower than sex offenders against adults on the WCST (deduction and cognitive flexibility) although they were significantly better on the COWAT (verbal fluency) and the Stroop test (control of internal interference). 

These results suggest that different subgroups of sex offenders might present different neuropsychological profiles. Surprisingly, both subgroups obtained comparable results on the trail-making B task although only the time variable (motor speed), not the number of errors (switching capacities) was available. But again, distribution of effect sizes was particularly wide for sex offenders against children. 

The distinction between nonpedophilic child molesters and exclusive pedophile child molesters, for instance, could be crucial in neuropsychology because the latter seem to be less cognitively impaired (... ...) 

Pedophilic child molesters might perform as well as controls (and better than nonpedophilic child molesters) on a wide variety of neuropsychological measures when mean IQ and other socioeconomic factors are similar (Schiffer & Vonlaufen, 2011). In fact, some pedophiles have higher IQ levels and more years of education compared with the general population (... ...)

Other potentially important distinctions such as preferential vs. situational or intrafamilial vs. extrafamilial sexual child abuse should be considered in neuropsychology as well. Given the growing number of neuropsychological studies that distinguish subgroups of sex offenders, it will soon be possible to test hypotheses of the sort (... ...)

Another interesting result was the confirmation that sex offenders against adults, as a group, tended to score similarly to non-sex offenders (inhibition and verbal deficits).
Future neuropsychological studies with more specific measures and participants might find difference between antisocial and deviant sex offenders against adults (e.g. generalized vs. specialized criminality).

If confirmed, results of this study suggest that more specific neuropsychological assessments might also help identify different risk factors associated with sexual offending, such as general delinquency (antisociality, impulsivity, and risk taking) or low social competence (asociality and poor higher order executive functioning). 

The opposite might also be true, as neuropsychological profiles of high impulsivity scores, low verbal capacities, and poor lower order executive functioning might predict higher risks for general but not sexual recidivism (McCann & Lussier, 2008). To this end, neuropsychological assessments should be based on more specific measures.

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Overall, this first meta-analysis of existing neuropsychological results regarding sex offenders yielded some interesting findings although available data were too few to test or confirm all of the hypotheses. 

The main goal was to define specific subgroups of sex offenders based on criminological typologies and to demonstrate that they present distinct cognitive profiles. Unfortunately, it was not possible for us to achieve this goal.

Consequently, it is currently impossible to say whether sex offenders present broad, nonspecific cognitive impairments or, instead, specific neuropsychological profiles.

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