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Adolescent Offenders & Using the PPG

Peter M Byrne, PhD


In April 2002, the Sex Offender Management Board wrote a protocol for use of the Penile Plethysmograph (PPG) with adolescents in the State of Colorado. After sending their proposed revisions to Peter M. Byrne, Ph.D., for his review, he wrote the following to provide his interpretation of research support for the changes that were suggested and eventually made. It is useful information for anyone interested in the topic:

1) The first issue is that there is a small, but growing published literature on the use of PPG procedures with adolescents. I have attached a bibliography below for your review and can also make hard copies of those studies available to you if you wish.
2) The two most recent published articles of which I am aware are those of Murphy, DiLillo, Haynes, & Steere (2001) and Seto, Lalumiere, & Blanchard (2000). These articles were published in the journal published by ATSA (Sexual Abuse: A Journal of Research and Treatment) and a journal published by the American Psychological Association (APA; Psychological Assessment), respectively. These journals have solid reputations. The ATSA journal is particularly germane to sexual offending assessment and treatment, while the APA journal has exceptionally high standards for sound methodology. I would like to discuss these two studies and their relationship to the proposed SOMB criteria.

The need for criteria: The linkage to risk for recidivism

The first point I would again submit is that not all juveniles who commit sexual offenses are in need of a penile plethysmograph test. Having said that, it is therefore important to develop research based criteria to identify those most likely to benefit from PPG evaluation. It is important to note that the mechanism to be utilized in developing these criteria is to try and identify criteria that pre-select those individuals who are more likely to have deviant arousal. For instance, the task before the Board is to develop criteria for those boys who are at higher risk for sexually reoffending. One of the best instruments with published data available today for examining risk for reoffense in juveniles is the Juvenile Sex Offender Assessment Protocol (J-SOAP: Prentky, Harris, Frizzell, & Righthand, 2000). The scale on the J-SOAP that is most associated with the presence or absence of deviant sexual arousal is Scale 1, the Sexual Drive/Preoccupation Items. It contains four items:

1) Prior legally charged offenses
2) Duration of sex offense history

3) Evidence of Sexual Preoccupation/obsessions
4) Degree of Planning

As one can see, there is no mention of victim gender in this classification and these four classifications are remarkably similar to the revisions implemented by the Board. The two published research studies, along with my research data, can be instructive in guiding this process.

Victim Gender and It’s Relation to PPG and Risk

From this point forward, the victim gender criterion as it relates to adolescent PPG and risk for recidivism will be my focus of attention. The victim gender criterion raised by Gail Ryan and she was correct in identifying to the board that those juveniles with male victims are those most likely to have deviant arousal. This finding was supported in Hunter et al’s (1994) research and also in the Murphy et. al. (2001) and Seto et al. (2000) studies. It is a strong and consistent finding. Clearly the presence of male prepubescent victims is a risk factor. But, what about those with female prepubescent victims? This is where the two most recent studies may also be of interest.

The first issue pertains to similarities and differences between adult and juvenile sexual offenders. It is an often cited finding from the adult field that deviant sexual arousal as measured by the PPG is the single best predictor of recidivism among those who molest children (Hanson & Bussiere, 1998). The main area of interest in this regard is the age of the victim. The vast majority of PPG research has been conducted on adults. Thus, one of the most important question is how similar is adolescent PPG to adult PPG?? The first thing to note from the Seto et al. adolescent PPG study is their conclusion:

“As usually found with adult offenders (Seto & Lalumiere, 2000), the pedophilic index scores [meaning presence of deviant arousal] of adolescent offenders against children were positively associated with having multiple victims, having a male victim, having very young victims, and having extrafamilial victims [italics mine](the correlations for the last two offense history variables did not reach statistical significance) (p. 326).”

In other words, their findings were similar to those from the adult field. The correlation between sexual deviance is stronger for those with male victims, but that DOES NOT mean there is NO correlation between deviance and those with female victims. For instance, in this case the two groups of adolescent offenders (one with male child victims and the other with female child victims) each had an N of only 14; thus, there likely was not enough statistical power to detect a significant correlation if one existed. It is likely that with more subjects the findings would have been significant because the more subjects in the design, the more statistically powerful the analysis. An example of this point is from Seto et al’s (2000) adult study that was comprised of over 700 subjects.

Another interesting facet of the Seto et al (2000) article is that they compared the deviance scores of “adolescents” (mean age 15-16), “young adults” (mean age approximately 19) and control groups of nonoffenders and rapists (both about 19). However, in the “young adult” group, who were only 3 years older, they found that those with only female victims DID have deviant arousal and this finding was consistent with other research from the adult literature (Hanson & Bussiere, 1998) regarding risk for sexual recidivism. The authors struggled with their findings, stating:

“The finding that adolescent offenders with only female child victims did not show pedophilic interests is surprising because, as a group, young adult offenders with only female child victims (who are on average just 3 years older than the adolescent offenders) did show pedophilic interests.”

The discrepant finding between the “young adult” and “adolescent” groups raises a number of important questions. Why would the 19 year olds with female victims be more pedophilic than similar 15-16 year olds?? There are a number of hypotheses that one could generate to address this question, including the statistical power issue related to earlier. My opinion is that those boys with female victims never dealt with the arousal issue from their offending behaviors and it then became crystallized into their arousal pattern as they developed, thus increasing their risk for reoffense. If the problem could be assessed and, then, if identified, treated at a younger age, we could perhaps “inoculate” these boys against future risk for sexual reoffending. From this perspective I would argue that it is imperative to include those with multiple female victims along with those with multiple male victims.

Murphy et al (2001) also studied the predictors of adolescents responding on the PPG and found that those with male victims tended to respond more on the PPG than did those with only female victims. However, they also point out that the relationship between having male victims and increased risk for recidivism within other adolescent literature this question is still somewhat unclear:

“…the relationship between victim gender and sexual reoffending is less clear. Smith and Monastersky (1986) and Langstrom and Grann (2000) both found a history of male victims was related to recidivism, whereas this was neither found by Worling and Curwen (2000) nor was it found by Rasmussen (1999). However, there were only a small number of recidivists in the Rasmussen study.”

Summary & Conclusions

In summary, it is clear that there is an established and growing literature on the use of PPG procedures with juvenile sexual offenders. A clear finding from this literature is that that those adolescents with male victims are most likely to have deviant arousal as measured by the PPG, and are thus clearly at higher risk. Thus, those with only female victims are at a lower risk, but are not absent of risk. It is a well-established finding from the adult literature that those with multiple and younger victims are at a higher risk for re-offending, and of particular concern is the finding of deviant arousal in the “young adult” group from the Seto study. Finally, it is important to note that one of the leading actuarial instruments (the J-SOAP) does not discriminate in terms of gender of the victim.
It is my opinion, therefore, that the standards as they are now constructed reflect an accurate method that is grounded in the most recent research by which the Board can reasonably identify in their standards those adolescents who are more at risk for reoffense in terms of the presence or absence of deviant sexual arousal.


Seto, M. C., Lalumiere, M. L., & Blanchard, R. (2000). The discriminative validity of a phallometric test for pedophilic interests among adolescent sex offenders against children. Psychological Assessment, 12, 319-327.

Murphy, W. D., DiLillo, D., Haynes, M. R., & Steere, E. (2001). An exploration of factors related to deviant sexual arousal among juvenile sex offenders. Sexual Abuse: A Journal of Research and Treatment, 13, 91-103.

Becker, J. V., Hunter, J. A., Goodwin, D., Kaplan, M. S., & Martinez, D. (1992). Test-retest reliability of audio-taped phallometric stimuli with adolescent sex offenders. Annals of Sex Research, 5, 45-51.

Becker, J. V., Hunter, J. A., Jr., Stein, R. M., & Kaplan, M. S. (1989). Factors associated with erection in adolescent sex offenders. Journal of Psychopathology and Behavioral Assessment, 11, 353-362.

Becker, J. V., Kaplan, M. S., & Tenke, C. E. (1992). The relationship ofabuse history, denial and erectile response profiles of adolescent sexual perpetrators. Behavior Therapy, 23, 87-97.

Becker, J. V., Stein, R. M., Kaplan, M. S., & Cunningham-Rathner, J.(1992). Erection response characteristics of adolescent sex offenders. Annals of Sex Research, 5, 81-86.

Hunter, J. A., Jr., & Becker, J. V. (1994). The role of deviant sexual arousal in juvenile sexual offending: Etiology, evaluation, and treatment. Criminal Justice and Behavior, 21, 132-149.

Hunter, J. A., Jr., Goodwin, D. W., & Becker, J. V. (1994). The relationship between phallometrically measured deviant sexual arousal and clinical characteristics in juvenile sexual offenders. Behaviour Research and Therapy, 32, 533-538.

Kaemingk, K. L., Koselka, M., Becker, J. V., & Kaplan, M. S. (1995). Age and adolescent sexual offender arousal. Sexual Abuse: A Journal of Research and Treatment, 17, 249-257.

Becker, J.V., Cunningham Rathner, J., Kaplan, M.S. (1986). Adolescent sexual offenders: Demographics, criminal and sexual histories, and recommendations for reducing future offenses. Journal of Interpersonal
Violence, 1, 431-445.

Becker, J.V., Harris, C.D., Sales, B.D. (1993). Juveniles who commit sexual offenses: A critical review of research. Nagayama Hall, Hirschman Graham and Zaragoza (Eds) In Sexual Aggression: Issues in etiology, assessment,and treatment (pp. 215-228). Taylor & Francis: Washington D.C.

Kaplan, M. S. & Becker, J.V. (1992). Adolescent perpetrators of incest. In Armen & Hersen (Eds) Assessment of Family Violence: A criminal and legalsourcebook (pp. 332-347). Wiley: New York.

Murphy, W.D., Haynes, M.R., & Page, I.J. (1992). Adolescent sex offenders. In O’Donahue & Geer (Eds) Sexual Abuse of Children: Theory & Research (pp.394-429).

Morenz, B., & Becker, J.V. (1995) The treatment of youthful sexual offenders. Applied and Preventive Psychology, 4, 247-256.

Zussman, R. (1989). Forensic evaluation of the adolescent sex offender. Forensic Reports, 2, 25-45.