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Title: Assessment of pedophilia
Author(s): Kurt Freund
Affiliation: Department of Psychiatry, University of Toronto
Citation: Freund, K., “Assessment of pedophilia,” in Cook, M. & Howells, K. (eds.), Adult sexual interest in children, London: Academic Press, 1981, pp. 139-179.


The author writes that “all sexual (or erotic) behavior is linked to reproduction,” but that this fact is insufficient for distinguishing between sexual and non-sexual behavior in an individual. He defines as sexual “those behavior patterns and stimulus configurations that usually occur together with ‘physiologic responses,’ specifically in the reproductive system.”

However, he notes that determining whether or not particular behavior is sexual is not always clear-cut. Both internal erotic motivators (e.g., hormonal) and external erotic stimuli (e.g., an attractive person) result in an increased erotic arousal level, which in turn results in erotic behavior.

The plethysmograph

The author introduced the penile plethysmograph in 1957 to “diagnose homosexuality” by measuring the extent to which a man’s penis became erect in response to his viewing photographs of nude men. The device had originally been developed in 1908 to study the behavior of dogs, and was first used on humans in 1934 to investigate erectile difficulties.

However, these earlier versions of the device could only detect whether or not the penis was erect; they could not measure varying degrees of arousal. The author’s version was the first that was able to do so.

In his original design, a glass or tin cylinder was placed over the penis, and an air-filled tube connected it to a measuring and recording device. As the penis became erect, its volume increased, and the volume of the surrounding air decreased. The resulting pressure change was transmitted to the recording device through the tube. This was referred to as the volumetric method.

Newer devices rely on measurement of penis circumference rather than volume. An elastic tube with very small diameter, filled with mercury, is placed around the penis, and electric current is passed through the tube. An increase in penile circumference causes elongation of the tube and an increase in electric resistance in the mercury, which is then detected by the recording instrument. Some versions use a sheet metal open ring in place of the elastic tube.

Over the years, numerous experimental developments have improved the accuracy and precision of the readings of the plethysmograph.

Most people respond sexually to a broad spectrum of external stimuli, from those that they prefer least to those they prefer most, creating a hierarchy of preferences. This hierarchy can be assessed by using the plethysmograph to measure the erotic value of various stimuli. Slides, films, and videos of naked adults and children have been used as stimuli, as well as audio recordings of simulated sexual activities.

Another method, developed by Abel, requires that the man describe a sexual experience or fantasy while the plethysmograph measures his erection. The experimenter or therapist notes the content of the man’s description which corresponds to an increasing erection, then elaborates on this content in a taped description which is used as a stimulus during the next plethysmograph session. This process can then be repeated again to get a third version of the fantasy, which is highly erotic for the individual.

The author’s experience is that when used on men who do not attempt to misinform, the plethysmograph is quite accurate at measuring arousal. However, it is possible (though difficult) to misinform, which very much limits the value of the device. Studies conducted in the 1960s and 1970s found that 10-50% of men could fake results (in both directions) by imagining stimuli other than what was shown to them. Faking was easier when the man had prior experience with the plethysmograph. Current research is being conducted to determine how faking can be detected or made more difficult.


The author defines pedophilia in a manner analogous to his definition of homosexuality: a sustained erotic preference for children up to and including the age of 11 or 12, over physically mature people, under free choice of a partner. Similarly, he defines hebephilia as a sustained erotic preference for pubescents up to and including the age of 13 or 14 for girls, and 15 or 16 for boys.

One of the author’s studies found that homosexual men attracted to men showed an average arousal response to pubescent boys that was 62% of their response to men, and arousal response to 9 to 11 year old boys that was 19% of their arousal level to men. Similarly, heterosexual men attracted to women showed arousal to pubescent girls that was 57% of their response to women, and arousal to 9 to 11 year old girls that was 34% of their arousal level to women.

The author turns to the issue of using the plethysmograph to validate treatment methods:

Among practitioners in the field, the opinion seems to prevail that there exist procedures capable of curing pedophilia, or which at least have a substantial beneficial effect on this disturbance. However, in therapeutic experiments, often either the definition of pedophilia or of therapeutic success, or both, are not well enough specified to warrant such a conclusion.

The typically used definition of pedophilia is inappropriately loose—anyone convicted for sexually approaching a child—so that situational offenders who are unlikely to re-offend regardless of therapy are labeled as pedophiles then pronounced cured. In addition, studies of the effectiveness of therapy do not include comparison groups of those who do not obtain therapy.

Furthermore, when studies claim to find substantial change in sexual response, there is no long-term follow up to distinguish between superficial, temporary change, and that which is permanent. Studies on homosexuals show that temporary change is easily produced.

A 1971 study assessed the effectiveness of aversion therapy on homosexuals. The study compared those who “showed improvement of sexual behavior” according to “sexual behavior ratings or reduction of homosexual attitudes” with those who did not show such “improvement.” There was no significant difference between the groups in penile response to pictures of males.

Two studies of homosexual pedophiles conducted in the 1970s found a decrease in penile response to pictures of boys after treatment, but continuing arousal by fantasies or activities with boys. Therapy in one study involved punishment for penile response to pictures of boys, while another study utilized “non-punishment procedures.”

Even when the plethysmograph seems to indicate that therapy is effective, one should not be too optimistic, since faking and other factors can cause a discrepancy between actual preferences and plethysmograph readings. A patient in therapy intended to change sexual feelings and attitudes will especially feel a demand to influence test outcomes in a favorable direction. Therefore, a method of using the plethysmograph that detects or prevents faking should be used.

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