Can phallometry help predict deviant sexual preferences and reduce sexual offences?

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Unsurprisingly, research shows that people who have deviant sexual preferences are more likely to commit sexual offences, so it makes sense that if we can more accurately identify deviant sexual preferences, we will be able to reduce crimes of this nature.

Phallometry (also known as penile plethysmography or phallometric assessment) involves placing a device around the penis to measure sexual arousal by assessing changes in penis circumference or blood volume in response to a range of auditory or visual stimuli. This method is used to diagnose offenders with deviant sexual preferences, such as those attracted to children, and to determine how well they have responded to treatment.

This rapid response report from the Canadian Agency for Drugs and Technologies in Health set out to answer three questions:

  1. What is the diagnostic accuracy of phallometric assessment of sex offenders?
  2. What is the comparative test accuracy of phallometric assessment versus other tools for risk assessment of sex offenders?
  3. What are the evidence-based guidelines and recommendations for risk assessment of sex offenders?

The authors conducted a systematic literature search, but only found 8 non-randomised studies to include in their review. The study population was primarily men who committed offences against children. The quality of the included studies was generally poor.

The authors concluded:

The results for the diagnostic accuracy of phallometric assessment were mixed. Two studies indicated that phallometric assessment could correctly distinguish paedophiles from other offenders, while one found correct assessment was dependent on the choice of victim. No relationship between individuals diagnosed by different methods was observed.

As a tool for risk assessment, phallometric assessment was generally useful for predicting recidivism (repeat offences), with the exception of one study. However, while study authors agree that phallometry is a useful tool for risk assessment, there is insufficient evidence to support its use over other methods.

No evidence-based guidelines for the diagnosis or risk assessment of sex offenders were identified.

Phallometric Assessment of Sex Offenders: A Review of the Clinical Evidence and Guidelines (PDF). Canadian Agency for Drugs and Technologies in Health, Sep 2011.

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