METHOD

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Subjects

The Kurt Freund Laboratory (formerly, Research Section of Behavioural Sexology) of the Centre for Addiction and Mental Health in Toronto, Ontario, Canada, conducts sexological assessments on male patients referred because of illegal or disturbing sexual behavior.

The centerpiece of these assessments is phallometric testing, a psycho-physiological technique for assessing erotic interests in male adults and adolescents. In this procedure, the individual’s penile blood volume is monitored while he is presented with a standardized set of laboratory stimuli depicting a variety of potentially erotic activities or objects. The patient’s penile blood volume increases (i.e., degrees of penile erection) are taken as an index of his relative attraction to the different classes of stimuli.

The great majority of patients are referred to the Laboratory by parole and probation officers, lawyers, correctional institutions, children’s protective societies, and so on, although some patients seek a referral on their own initiative.

During the years when he headed this service (1969–95), Kurt Freund, M.D., D.Sc. (deceased) gave versions of the same self-administered, paper-and-pencil questionnaire to virtually all patients capable of completing it

(i.e., those with sufficient English-language skills and intellectual capacity).

This questionnaire, the Erotic Preferences Examination Scheme (EPES) was never published in its

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entirety, although scales composed of items from it have been published in a variety of places

(e.g., Blanchard, 1989, 1998; Freund, 1981; Freund & Blanchard, 1983, 1998).

Beginning with the last major revision of the EPES (1974) until its replacement with a different instrument (1995), the patients’ responses to the EPES were archived in a computerized database, along with their phallometric test results.

The EPES included four items concerning childhood episodes of unconsciousness with or without obvious traumatic causes. The database was searched for all subjects who answered one or more of these items

(over 99% of subjects who answered one of them answered all four),

and who produced valid results on either of the two versions of the phallometric test most frequently used during this period for assessing patients’ erotic interest in persons of different ages. These will be referred to as the “nine-category version” and the “five-category version,” for reasons that will become clear later.

This retrieval extracted 1206 subjects. These had a mean age of 34.88 years (SD = 11.68). Subjects indicated their educational level on one item of the EPES by endorsing one of seven response-options, ranging from no formal education to university graduation. Their median educational level was more than 8 but fewer than 12 grades completed.

The known sex offenses involved prepubescent girls for 50% of the subjects, pubescent girls for 18%, adult women for 16%, prepubescent boys for 26%, pubescent boys for 33%, and adult men for 3%. These percentages add up to more than 100%, because some subjects had sex offenses in more than one category.

There were 902 subjects who had valid results on the nine-category version of the phallometric test, and 304 subjects who did not have valid results on the nine-category version but did have valid results on the five-category version.

Materials and Procedure

Intelligence Rating

All subjects underwent a semi-structured interview, which was conducted, in the great majority of cases, by Dr. Freund himself. In these interviews, standard pieces of information were collected for clinical purposes and for storage in the previously mentioned database.

Of present interest was the interviewer’s global impression of the patient’s intelligence. This was based on the patient’s personal, educational, and employment histories and his clinical presentation in interview, plus whatever other information was available

(e.g.,

The recorded estimate employed a 6-point rating scale:

Basic Phallometric Procedure

The phallometric apparatus and the basic procedures used with this study’s subjects are the same as those used in the Kurt Freund Laboratory today. This laboratory is equipped for volumetric plethysmography; that is, the apparatus measures penile blood volume change rather than penile circumference change. The volumetric method measures penile tumescence more accurately at low levels of response

(Kuban, Barbaree, & Blanchard, 1999).

The construction and operating principles of the volumetric equipment have previously been described in several places

(e.g., Blanchard, Klassen, Dickey, Kuban, & Blak, 2001).

The examinee puts the volumetric sensor over his penis, according to instructions from the test administrator. He then sits in a reclining chair, which faces three adjacent projection screens

(sometimes only one projection screen, in early subversions of the tests analyzed in this paper).

After the set-up is complete, the examinee’s lower body is covered with a sheet to minimize his embarrassment or discomfort. During the test, the examinee’s face is monitored by a low-light video camera, in order to monitor stimulus avoidance strategies such as closing the eyes or averting them from the test stimuli.

The test stimuli are presented in discrete trials. Each trial presents stimuli from one and only one class, although several exemplars of that class (e.g., prepubescent boys) may be included in the same trial. The trials are arranged into blocks, with each block including one trial of each type in fixed pseudorandom order. Although the length of the trials is fixed, the interval between trials varies, because penile blood volume must return to its baseline (flaccid) value before a new trial is started. The time required to complete a test is usually about 1 hr.

Recording of penile blood volume begins 5 s before trial onset and ends 5 s after trial offset. The pre- and post-trial data are not, however, used in any computations; therefore the trial response does not reflect recovery (i.e., detumescence) rates. Penile blood volume change is sampled four times per second. The examinee’s response is quantified in two ways: as the extremum of the curve of blood volume change

(i.e., the greatest departure from initial value occurring during the trial),

and as the area under the curve.

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To identify examinees whose penile blood volume changes during the test trials remain within the range typical of random blood volume fluctuations in non-aroused subjects, the mean of the three highest positive extremum scores — a quantity called the Output Index (Freund, 1967) — is calculated.

In the present study, the phallometric data of subjects who failed to meet a criterion output index of 1.0 cm³ — the criterion currently used in the Laboratory — were excluded as invalid.

Each examinee’s extremum scores are then converted into standard scores, based only on his own extremum data, and the same operation is carried out on his area scores.

Next, for each examinee, the standardized extremum and area scores are combined to yield a separate composite score for each of the trials, using the formula

( z^E_i + z^A_i ) / 2, where z^E_i is the standardized extremum score for the i th trial and  z^A_i is the standardized area score for the i th trial. These operations are carried out for the following reasons

(Earls, Quinsey, & Castonguay, 1987; Harris, Rice, Quinsey, Chaplin, &Earls, 1992; Langevin, 1985).

(Freund, Scher, & Hucker, 1983).

In the last stage of basic processing, the data are reduced to a set of final scores for each examinee by averaging his composite scores in each of the stimulus categories.

These category scores are taken as measures of the examinee’s relative erotic interest in adult women, pubescent girls, prepubescent girls, and so on.

Nine-Category Test Version

The specific features of the nine- and five-category test versions have previously been described, and data from them have previously been published

(e.g., Freund & Blanchard, 1989; Freund & Watson, 1991).

Those studies were concerned with the accuracy of the phallometric test in diagnosing pedophilia, and none of them examined the variables of interest in the present study. In this version of the test, the stimuli were 28-s film clips of nude adults or children smiling and walking slowly toward the camera

(but not engaging in any overtly sexual or even flirtatious behavior).

These stimuli included eightcategories of human types: physically mature women, pubescent girls, 9–11-year-old girls, and 5–8-year-old girls, and four corresponding categories of males. The ninth stimulus category (“neutral”) consisted of film clips of landscapes (waves crashing on a beach, etc.), with no human beings in evidence.

The test consisted of three blocks of nine trials. Following the general procedure described earlier, each block included one trial of each type in fixed pseudorandom order.

Five-Category Test Version

This differed from the nine-category version in the modality of the test stimuli as well as the number of different stimulus categories. The stimuli were audio-taped narratives presented through headphones and accompanied by slides shown on projection screens. There were five categories of narratives, which described sexual interactions with prepubescent girls, adult women, prepubescent boys, and adult men, and also solitary, nonsexual activities (“neutral” stimuli).

All narratives were written in the second person and present tense

(e.g., “You are babysitting a five-year-old girl for the evening. She is taking a bath before she gets ready for bed. Through the open bathroom door, she calls you to come in and scrub her back ...”)

and were approximately 100 words long. The narratives describing heterosexual interactions were recorded with a woman’s voice, and those describing homosexual interactions, with a man’s. Neutral stimuli were recorded with both.

Each test trial consisted of one narrative, accompanied by photographic slides that showed nude models corresponding in age and gender to the topic of the narrative. Neutral narratives were ac-companied by slides of landscapes. The test consisted of five blocks of five trials, with each trial being 54 s long.