Penile Plethysmograph (PPG)

The penile plethysmograph (PPG) is an assessment method that can be used to detect sexual deviancy.  

In order to maximize the likelihood that risk assessments are as accurate as possible and interventions are effective with sex offenders,  treatment should focus on the changeable factors that are known to be associated with sexual recidivism (i.e., criminogenic needs).  Current research indicates that sexual deviancy is the predictor of future sexual offending, and thus an important issue to target in treatment.  It is however difficult to assess. 

Many individuals who commit sexual offences do not display deviant interests and some are likely to deny such interest.  The PPG provides a method of evaluating sexual deviancy.

The PPG involves monitoring of the offender’s penile responses (often along with other psychological and psychophysiological responses) whilst he views visual material or listens to auditory material depicting (a) scenarios relevant to his offending and (b) scenarios of alternative, legally acceptable behaviours, e.g. consenting adult sexual behaviour.  The FPC utilises audio material as stimuli for the PPG.  The PPG cannot be used to establish a participant’s guilt or innocence in relation to a particular offence or offences.  The FPC utilises PPG for the following clinical purposes: 

1. To provide a method of assessing for sexual deviancy;
2. To facilitate participant acknowledgement of their sexual arousal/interests and their engagement in treatment;
3. To assist with the development of a formulation of problematic or offence-related sexual behaviour;
4. To assist treatment planning and risk management decisions; and
5. To assist measurement of changes in sexual arousal/interest.

Guidelines for the Use of the Penile Plethysmograph

FPC strictly complies with the British Psychological Society's established guidelines which were published in 2008.

These brief guidelines are intended to inform good practice in the penile plethysmograph assessment, while allowing for the exercise of professional judgement in particular situations. They should be read in conjunction with existing guidelines on professional conduct published by the Society and articles on penile plethysmography assessment in the scientific and professional literature.  The psychologist should have up-to-date knowledge of relevant practice, legal issues and literature. Staff participating in this work at any level should be adequately briefed and have the option not to be involved should they find the procedure or material distressing.

The penile plethysmography test should be carried out only in the context of an appropriate range of other assessment and treatment procedures or in the course of research that has been professionally and ethically approved by the relevant body. Selection of the stimuli should take into account ethical consideration of how the material was produced or obtained, e.g. if it was under abusive circumstances. Selection of penile plethysmography stimuli (content and mode of presentation) should take into account an appropriate balance between obtaining the best possible assessment and risk of exposing the subject to material which may be therapeutically counter-productive if it is outside their own suspected or known experience. The psychologist should brief the subject on the purpose and procedures involved in penile plethysmography assessment including possible results and their interpretation. He/she should explain limits of confidentiality and likely consequences of participation, non-participation and withdrawal and check that the subject has understood.

Debriefing should be carried out at the end of each assessment. This should include consideration of the impact of the assessment on the client and the need for support and advice. A record that the subject has been properly briefed/debriefed should be kept where appropriate. Stimuli material for the penile plethysmograph assessment should be kept secure and access limited to those using it for professional purposes. Assessment should only be carried out in appropriate physical conditions with due regard to the standards of safety, privacy, comfort and current hygiene recommendations.