Neil P. Naik1, Jennifer Sin Yan Too1, Allan Jenkinson1, Sharifah Syed Adnan1, Wai In Wong1, Amara Anyiam1

Author affiliations
1RCSI medical student

Royal College of Surgeons in Ireland Student Medical Journal 2012;5: 58-60.

Background: In 2004, Seto et al. investigated whether Screening Scale for Paedophilic Interests (SSPI) scores correlate significantly with phallometric responses and sexual recidivism among offenders with child victims in two study groups of adult sex offenders with child victims.1 This paper aims to analyse the ethical aspects of the study, specifically the vulnerability of the group of participants used and the use of phallometry in research.
Ethical appraisal: The study poses several ethical controversies regarding the selection of prisoners for investigation. In this study, no steps were taken to safeguard the rights and freedoms of those who participated. In addition, whether informed written consent was obtained for either study is questionable. The use of child sexual images and the physical and mental intrusion on participants may also be unethical, as the study does not state whether consent for either of these aspects of phallometry were obtained.
Recent developments: Since Seto et al.’s study on prisoner phallometry and SSPI comparison, many advances in the field have taken place. Newer screening tools are being developed that are more predictive of recidivism than the SSPI, such as the Violence Risk Scale – Sexual Offender (VRS-SO).

“Researchers and clinicians are interested in paedophilic sexual interests because of their implicit or explicit theories that many sexual offences against children are motivated by such interests.”
– Seto et al.1

Paedophilic sexual interest is believed to be the underlying drive of sex offenders against children and the strongest known predictor of sexual recidivism.2,3 Phallometric (plethysmographic) testing is a research instrument used to provide insights into paedophilic sexual interests through its ability to identify paedophiles and predict sexual recidivism.4 Phallometry measures the erectile responses that occur when men are presented with visual and/or auditory sexual stimuli depicting children or adults.5 Phallometrically measured paedophilia in male prisoners and sexual recidivism is associated with four consistent variables: male victims; more than one victim; younger victims; and, extra-familial victims.3,6

The Screening Scale for Paedophilic Interests (SSPI), developed in 2001, incorporates these variables, thus reducing the need for phallometric testing.3

The SSPI was developed as a quick and easy-to-use scale to help identify individuals with paedophilic interests for the purposes of triage and risk management when phallometric testing or previously obtained phallometric data was unavailable.3 This scale was positively and significantly correlated with phallometrically measured paedophilic interests in a large sample of 1,113 sex offenders against children.3 A follow-up study showed that SSPI scores were positively correlated with a phallometric index of relative sexual arousal to prepubescent children among adolescent male sex offenders.7

This ethical review analyses Seto et al.’s study, which investigates if SSPI scores correlate to sexual recidivism among two samples of adult sex offenders with child victims.1 The implications of the study suggest that when determining whether an individual has recidivistic paedophilic sexual interests, surveys and history-based examinations can be used in place of phallometric tests. There were two studies carried out in this investigation involving adult male sex offenders with a history of child victims; the first study evaluated 113 adult males and the second evaluated 145. Both studies used cluster sampling by selecting the prisoners and offenders from Canada. In both studies, researchers correlated SSPI with phallometry and other scales, which included: Psychopathy Checklist-Revised (PCL-R); Rapid Risk Assessment of Sexual Recidivism; and, Sex Offender Risk Appraisal Guide (SORAG). Phallometry was measured using a mercury-in-silastic strain gauge.

Phallometry is intrusive, can be difficult to conduct and is unavailable in some clinical research laboratories.1,3,7 In situations where prioritising or making quick decisions on cases is essential, a simple historical measure that can assess paedophilic sexual interests would be of great value.1,3

Ethical appraisal of the study

Participants and informed consent
Prisoners are controversial participants to choose for a study. The Australian National Health and Medical Research Council describes prisoners as being in a “dependent or unequal relationship”.8 They constitute a category of people who are vulnerable in research studies due to coercion and preferential treatment between the prison administration and the prisoners.9 In this study, no steps were outlined to safeguard the rights and freedoms of those who participated. Likewise, one cannot be sure if there was discriminatory or preferential treatment of prisoners who participated in the study compared to those who did not.
For research to be ethical, regardless of the vulnerability of the participant group, informed consent must be ensured. A correct and ethical consensual process is described in the first study, which culminated in participants giving written informed consent. However, in the second study, obtaining informed consent was not mentioned and there is no evidence of written informed consent. Consent may have been implied in Study 2, but it should have been made clearer given the sensitive nature of the use of phallometry in a prisoner population.

Phallometry (plethysmography)
There are two important ethical issues around the use of phallometry, namely the use of child sexual images, and the physical and mental intrusion on participants.

Child sexual images
Regarding the use of child images in phallometric testing, Olsen et al. argue: “Children cannot give permission for their nude pictures to be used as stimuli in plethysmographic assessments; therefore, any use of nude child images constitutes exploitation of children and their pictures may not be used”.10 While obtaining consent from the parents for the use of child sexual images may have been legal, one may still argue that it is unethical to use child pornography.

The UN Convention on the Rights of the Child (1989) enshrines the child’s right to have an opinion taken into account, to obtain information and to have beliefs.11 However, most states rule that parents have the right to consent to having nude pictures taken and the subsequent use of them.10 While parents are responsible for their child’s well-being, it is debatable as to whether a parent can consent to the use of a child’s body for scientific purposes.

Olsen et al. have described the efficacy of these visual stimuli, explaining that visual images elicit responses from offenders where auditory stimuli fail to do so.10 The use of these images challenges the idea of maintaining the little autonomy a child may have, especially that of a pubescent child, as by law the decision is made by the child’s parents or guardians. In those cases where consent is given, one might argue that a prepubescent child may still be naive to the nature of the images for which he/she is posing, and thus cannot grant informed consent. This argument, however, is not applicable to pubescent children.

In 2001, a researcher attempted to create ‘ethically pure’ material by taking pictures of children in nudist camps. However, clinicians and researchers were still uncomfortable with holding these images.12 Recently, a Canadian private company produced ‘ethically acceptable’ images by creating computer-generated pictures without using real child photographs. However, these manufactured images are still considered illegal in some jurisdictions.12 Regarding this study, Seto et al. never discussed how the images used in the investigation were obtained, thus raising the question whether these images were ethically obtained.

Physical and mental intrusion on participants
The prisoners in the first study gave consent for the ‘use of their information’. It is not clear as to whether they were aware of the fact that phallometric testing was to be used. It is imperative that informed consent is obtained for this, as phallometric testing involves the physical and mental violation of the subject. Judge Noonan’s opinion regarding Judge Berzoc’s ruling in United States v. Weber – where the defendant was convicted and was to undergo “psychological/ psychiatric counselling and/or a sex offender treatment program” – sums up several key ethical issues in the use of phallometry.13 Regarding phallometry, Judge Noonan writes: “The procedure violates a prisoner’s bodily integrity by affecting his genitals. The procedure violates a prisoner’s mental integrity by intruding images into his brain. The procedure violates a prisoner’s moral integrity by requiring him to masturbate”.13

If fully informed consent is given, then technically there is no violation of a prisoner’s integrity. However, if no consent or consent without information is given, as one may suspect occurred in the second study, then the test is a serious violation of a person’s autonomy and integrity, as it implies that the prisoners were forced to take part in the research.

Seto et al. aimed to show that the SSPI would accurately predict recidivism and provide an alternative to more controversial and undesirable means – that is, phallometry and the use of child sexual images. Should this research produce positive results, it would mean that phallometry could be rendered obsolete in assessing sexual recidivism. Thus, one must ask oneself: is it right to allow these participants to engage in this ethically contentious study so that we will have more ethically sound techniques in the future?

During the time that this study was conducted, alternatives to phallometry would have included measuring the reaction time to visual stimuli and comparing the amount of time a participant looks at sexual versus non-sexual stimuli.14 A variant of this alternative is the Abel Assessment for Sexual Interest (AASI), which measures the amount of time an individual looks at clothed individuals in different contexts.14 However, despite the fact that the results were statistically significant, this test is not reliable because, as the authors assert, a high probability is not equivalent to certainty.14 Despite this shortcoming, one may argue that the use of the AASI instead of phallometry may have been preferable as it would not have required the use of child pornography or the violation of the subjects’ integrity.

Recent developments

Since the publication of Seto et al.’s study on SSPI and sexual recidivism, there have been several advances in the field. Critics claim that the SSPI overlooks some key aspects. An alternative scale, the Violence Risk Scale – Sexual Offender (VRS-SO), was developed in 2009 and was demonstrably more encompassing of the factors necessary in predicting recidivism.

Variables that were not included in the SSPI included denial of paedophilia and watching child pornography, which have been shown to increase the risk of recidivism.15,16 Denial was shown to be associated with increased sexual recidivism among low-risk (incest) offenders and decreased recidivism among high-risk offenders (i.e., those with extra-familial victims).15 Statistics indicate that the frequency of viewing pornography is primarily a risk factor for higher-risk offenders.16 Kingston et al. showed that watching pornography significantly correlated with recidivism. However, it is important to note that while offenders who watch child pornography show a high rate of re-offending, viewing child pornography alone does not increase the risk for committing hands-on sex offences in those who have never done so.17 Other screening initiatives have been developed for measuring sexual deviance that are more predictive of recidivism than the SSPI. Notwithstanding this, the SSPI has been used as a base scale to demonstrate the effectiveness of these tools. Canales et al. aimed to examine the construct validity of the VRS-SO screening tool for measuring sexual deviance.18 This is an offender risk assessment and treatment planning tool that assesses factors that correlate with an increased risk of sexual recidivism (sexual deviance, criminality and treatment responsivity). The SSPI was shown to correlate positively and significantly with the sexual deviance factor and treatment responsivity, and negatively with criminality.18 The VRS-SO takes into account more factors that are predictive of recidivism, and thus may eliminate the need for physically and mentally invasive phallometric testing.18


  1. Seto MC, Harris GT, Rice ME, Barbaree HE. The Screening Scale for Paedophilic Interests predicts recidivism among adult sex offenders with child victims. Arch Sex Behav. 2004;33(5):455-66.
  2. Hanson RK, Bussiere MT. Predicting relapse: a meta-analysis of sexual offender recidivism studies. J Consult Clin Psychol. 1998;66(2):348-62.
  3. Seto MC, Lalumiere ML. A brief screening scale to identify paedophilic interests among child molesters. Sex Abuse. 2001;13(1):15-25.
  4. Blanchard R, Klassen P, Dickey R, Kuban ME, Blak T. Sensitivity and specificity of the phallometric test for paedophilia in nonadmitting sex offenders. Psychol Assess. 2001;13(1):118-26.
  5. Seto MC, Lalumiere ML, Blanchard R. The discriminative validity of a phallometric test for paedophilic interests among adolescent sex offenders against children. Psychol Assess. 2000;12(3):319-27.
  6. Prentky RA, Knight RA, Lee AF. Risk factors associated with recidivism among extrafamilial child molesters. J Consult Clin Psychol. 1997;65(1):141-9.
  7. Seto MC, Murphy WD, Page J, Ennis L. Detecting anomalous sexual interests in juvenile sex offenders. Ann N Y Acad Sci. 2003;989:118-30.
  8. National Health and Medical Research Council. National Statement on Ethical Conduct in Human Research (2007): Chapter 4.3: People in Dependent or Unequal Relationships. 1-12-2009. Australian Government. Ref type: online source.
  9. Violence against women and girls in prison. Geneva; Quaker United Nations Office. October 6, 2005.
  10. Card RD, Olsen SE. Visual plethysmograph stimuli involving children: rethinking some quasi-logical issues. Sex Abuse. 1996;8(4):267-71.
  11. UNICEF. Fact sheet: A summary of the rights under the Convention on the Rights of the Child. 1989.
  12. Merdian H, Jones D. Phallometric assessment of sexual arousal. In: Boer D, Eher R, Craig L, Miner M, Pfäfflin F (eds.). International Perspectives on the Assessment and Treatment of Sexual Offenders: Theory, Practice, and Research.Oxford; John Wiley & Sons Ltd, 2011:141-70.
  13. Stratton M, Libby J, Yang D, O’Brien T, Corbet J. United States of America v. Matthew Henry Weber. 6797[05-50191], 6802-6831. 20-6-2006. United States Court of Appeals for the Ninth Circuit. Ref type: case.
  14. Taylor M, Quayle E. Adult sexual interest in children. Child Pornography: an Internet crime. New York; Brunner-Routledge, 2003:47-73.
  15. Nunes KL, Hanson RK, Firestone P, Moulden HM, Greenberg DM, Bradford JM. Denial predicts recidivism for some sexual offenders. Sex Abuse. 2007;19(2):91-105.
  16. Kingston DA, Fedoroff P, Firestone P, Curry S, Bradford JM. Pornography use and sexual aggression: the impact of frequency and type of pornography use on recidivism among sexual offenders. Aggress Behav. 2008;34(4):341-51.
  17. Endrass J, Urbaniok F, Hammermeister LC, Benz C, Elbert T, Laubacher A et al. The consumption of internet child pornography and violent and sex offending. BMC Psychiatry. 2009;9:43.
  18. Canales DD, Olver ME, Wong SC. Construct validity of the Violence Risk Scale – Sexual Offender Version for measuring sexual deviance. Sex Abuse. 2009;21(4):474-92.

Back to list of articles.