Pedophilia and IQ: more research needed

James Cantor is a psychologist who has popularized the notion that pedophiles have low IQ. I will show that this is based on a single study, not supported by other research, and should not be considered a settled matter.

The 2004 study

The foundation of Dr. Cantor’s claim is Cantor et al. (2004). Dr. Cantor and colleagues analyzed an expanded version of the same sample (p. 290) in Blanchard et al. (2007). These studies are generally high quality, but have never been reproduced. A substantial portion of primary research is known to be false, even when there are no obvious flaws in the methodology (Ioannidis, 2005). Only 64.6% of published independent replication attempts in psychology confirm the original results (Makel et al., 2012), and this is likely overestimated by the file-drawer effect. For this reason, it’s critical that findings be independently reproduced, especially in a field with as many variables as psychology.

The major problem with this study, in my view, is that it used a non-equivalent control group. The pedophiles were largely child molesters; there were some child pornography users in the sample, but they had higher IQ (Blanchard et al., 2007, p. 297). The closest possible comparison group would be non-pedophilic child molesters. Instead, Dr. Cantor used general sexology patients as controls, specifically excluding ones with offenses against children. His concern was that some child molesters who measure as non-pedophilic during phallometry might simply be suppressing their arousal. However, phallometry can reliably distinguish groups of pedophiles from non-pedophiles (Blanchard et al., 2001), so even if there were a few pedophiles hidden in the control group, it would not be enough to conceal any group difference in IQ.

The 2005 meta-analysis

In addition to the 2004 study, Dr. Cantor cites his later meta-analysis, Cantor et al. (2005), to support the IQ association. The problem is that this meta-analysis did not actually compare pedophiles to non-pedophiles. Instead, it examined three proxy variables that are known to associate with pedophilia in child molesters: victim age, victim gender, and victim relationship. Compared to non-pedophilic child molesters, pedophilic molesters are more likely to have younger victims, male victims, and extrafamilial victims. Consequently, if pedophiles have low IQ, one would expect child molesters with young, male, or extrafamilial victims to have low IQ. The single best indicator of pedophilia in child molesters is having a male victim; Seto & Lalumière (2001) found it was twice as reliable as victim age based on a sample of over 1000 offenders (p. 20).

Dr. Cantor’s meta-analysis found that offenders with younger victims had lower IQ, but there was no correlation between IQ and victim gender or relationship (p. 561). Two of three proxy variables, including the most important, gender, did not support his hypothesis. Contary to Dr. Cantor, I interpret this as strong evidence against his hypothesis, since there are other obvious explanations for the relationship between IQ and victim age (e.g., younger victims are easier targets for low-functioning molesters).

Contradicting research

A number of studies have found that pedophiles have normal IQ. These studies differ from Cantor et al. (2004) in that they include non-pedophilic child molesters as controls, and some exclude subjects with mental retardation from both groups. Although these findings put Dr. Cantor’s claim in question, the sample sizes are too small to settle the matter. I should also point out that both Dr. Cantor’s study (Cantor et al., 2004, p. 5) and the studies below did not administer full IQ tests; they estimated IQ using simpler tests. These simpler tests are likely sufficient to detect group differences.

  • Eastvold et al. (2011): “PEDs [pedophilic child molesters] had a higher IQ than NSOs [nonsexual criminal offenders] (p = .014), and there was a trend for NPEDs [non-pedophilic child molesters] to have a higher IQ than NSOs (p = .051). PEDs also had better SK [semantic knowledge] than NSOs (p = .035).”
  • Schiffer & Vonlaufen (2011): “no significant difference in intelligence quotient (IQ) levels between all groups”. Pedophilic child molesters: 108.5; Non-pedophilic child molesters: 107.5; Forensic controls: 103.2; Healthy controls: 110.2
  • Suchy et al. (2009): No significant differences. Pedophilic child molesters: 106.59; Non-pedophilic child molesters: 102.05; Community controls: 105.62
  • Strassberg et al. (2012): This study used two samples. Sample one: “The 3 groups (PEDs, N-PEDs, CNTs) did not differ on […] estimated IQ (M = 104.6, SD = 8.1, range, 84–121)”. Sample two: “There was a significant difference among the groups on estimated IQ; the criminal controls scored significantly lower in IQ (M = 96.92, SD = 9.94) than either the pedophilic child molesters (M = 105.89, SD = 11.32) or nonpedophilic child molesters (M = 104.46, SD = 12.57). The 2 child molester groups did not differ significantly on estimated IQ.”

I am not alone in believing that these findings undermine the relationship between pedophilia and IQ. Eastvold et al. (2011) write,

“Importantly, this study sample was remarkably similar to our previous sample (Suchy et al., 2009a, 2009b). In both samples, IQs and semantic knowledge (SK) were average, with PEDs’ IQ and SK being slightly (nonsignificantly) higher than those of NPEDs, in the context of approximately 13 years of education for both groups. The IQ and SK of child molesters in the present study were slightly higher than those of NSOs. This appears to contradict published reports documenting positive correlations between IQs and victim age (Blanchard et al., 2007; Cantor et al., 2004; Cantor, Blanchard, et al., 2005). However, such findings may be misleading and can likely be explained by the heterogeneity of study samples and inclusion of individuals with mental retardation. The only other reported comparison between pedophilic and nonpedophilic child molesters (Blanchard et al., 2007) found no IQ differences, consistent with our findings. Further examination of phallometrically defined non-mentally retarded pedophilic and nonpedophilic child molesters would likely continue to dispute relationships between pedophilia and lower IQs.”

The bottom line

There is not enough evidence to make any conclusion about the IQ of pedophiles. One study supports a connection, but several others do not, including, in my opinion, Dr. Cantor’s own meta-analysis. Of course, Dr. Cantor’s thesis is plausible, and we can’t reject the possibility just because it’s unpleasant. The important thing to keep in mind is that, even if the association exists, it’s only the center of a bell curve. It says nothing about the intelligence of any given pedophile. Even if some pedophiles have lower IQ, many do not. Unfortunately, Dr. Cantor never emphasizes this to the media. He must know that the public always misinterprets this sort of statistic. When he explains the association between height, handedness and pedophilia, he often adds that it doesn’t mean short, left-handed people are pedophiles. Why doesn’t he give pedophiles the same consideration?


  • Blanchard R., Klassen P., Dickey R., Kuban M.E., Blak T. (2001). “Sensitivity and specificity of the phallometric test for pedophilia in nonadmitting sex offenders,” Psychological Assessment, 13 (1): 118-126
  • Blanchard R., Kolla N. J., Cantor J. M., Klassen P. E., Dickey R., Kuban M. E., Blak T. (2007). “IQ, handedness, and pedophilia in adult male patients stratified by referral source,” Sexual Abuse: A Journal of Research and Treatment, 19 (3): 285–309.
  • Cantor J.M., Blanchard R., Christensen B.K., Dickey R., Klassen P.E., Beckstead A.L., Blak T., Kuban M.E. (2004). “Intelligence, memory, and handedness in pedophilia,” Neuropsychology, 18 (1): 3–14.
  • Cantor J.M., Blanchard R., Robichaud L.K., Christensen B.K. (2005). “Quantitative reanalysis of aggregate data on IQ in sexual offenders,” Psychological Bulletin, 131 (4): 555–568.
  • Eastvold A., Suchy Y., Strassberg D. (2011). “Executive function profiles of pedophilic and nonpedophilic child molesters,” Journal of the International Neuropsychological Society, 17 (2), 295-307.
  • Ioannidis J.P.A. (2005). “Why most published research findings are false,” PloS MEDICINE, 2, 696–701
  • Makel M., Plucker J., Hegarty B. (2012). “Replications in psychology research: How often do they really occur?,” Perspectives on Psychological Science, 7: 537–542.
  • Schiffer B., Vonlaufen C. (2011). “Executive dysfunctions in pedophilic and nonpedophilic child molesters,” Journal of Sexual Medicine, 8: 1975–1984.
  • Seto, M.C., Lalumière M.L. (2001). “A Brief Screening Scale to Identify Pedophilic Interests Among Child Molesters,” Sexual Abuse, 13 (1): 15-25.
  • Strassberg D., Eastvold A., Kenney J.W., Suchy Y. (2012). “Psychopathy among pedophilic and nonpedophilic child molesters.” Child Abuse & Neglect, 36: 379–382.
  • Suchy Y., Whittaker W.J., Strassberg D., Eastvold A. (2009). “Facial and Prosodic Affect Recognition Among Pedophilic and Nonpedophilic Criminal Child Molesters”. Sexual Abuse, 21 (1): 93–110.
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