Penile Plethysmograph (PPG) in Criminal Cases

The penile plethysmograph (PPG) is a penile sexual arousal test that is often used to help determine whether a male participant is likely or unlikely to respond sexually to a child or adolescent. The results may be used in arriving at an opinion as to whether a person is a likely sex offender or is likely to reoffend. In some cases, it may be a requirement for a convicted individual to comply with conditions of supervised release. A defense attorney may enlist clinicians to administer the test to aid in the defense of child sexual abuse cases, such as Indecency with a Child.

What Is It?

Although the procedure is somewhat invasive to individual privacy, steps should be taken to minimize the impact and maintain as much dignity as possible for the participant. For example, the clinician who administers the test should not be in the same room. The individual who is undergoing the PPG is usually instructed to avoid masturbating for 24 hours prior to the test. According to the National Institutes of Health, volume or circumferential measurements may be used. The volume device uses an air-filled cylinder that displaces air when penile size increases, and the circumferential method uses an expandable cuff that measures any size increase. In both cases, penile size changes are measured in response to sexual stimuli. Clinicians may use images, audio, videos and other stimuli. In searching other resources you may see alternative terms used: phallometry, or erectometer.

What Happens During Testing?

When a person arrives for the assessment appointment, the clinician who administers the test explains the entire procedure first. The clinician leaves the room, and the test participant must pull down his pants and underwear before he sits down. Using the clinician’s instructions, the participant applies the measurement device. It is fitted around the shaft of the penis. One procedure that may be used is the setting of a ceiling measurement, which is the participant’s penile circumference at full arousal. Self-stimulation may be used to achieve this state. However, the test will not officially begin until the participant reaches a completely non-erect state. According to the National Institutes of Health (NIH), many clinicians use slides of clothed children and adults. Clinicians may use audio or video stimuli with certain sounds or scenarios. Participants may rate their level of sexual arousal or response in a self-reporting format during the test, and the test administrator uses the self-reported information to compare with physical responses. Post-test questions and responses are collected for analysis.

PPG tests are designed to allow for coughing or shifting. Those actions are factored in to ensure a more accurate outcome in determining whether any minor changes are related to the stimuli or something else. Testing may include the use of respirator bands and fingertip sensors to measure responses of anxiety, sweating and changing breathing patterns during the procedure. PPG testing has been used on humans since the 1930s and has no known significant safety issues. The devices do not deliver an electric shock or create physical pain. Since the devices are thoroughly disinfected and sanitized between participants, they do not pose sanitation risks.

Courts have reached different conclusions about the level of accuracy of penile plethysmography as reported in the scientific literature. Generally, there is legal, scientific, and academic debate about the reliability of the PPG. An attorney hoping to use PPG results should take care and make an effort to establish evidence supporting the efficacy of this test. There may be less invasive measures with comparable or greater reliability.

Use in Sex Offender Treatment

In post-conviction applications, the PPG is meant to help determine the risk of recidivism for people who are convicted of sex crimes. The test is usually performed after the individual undergoes therapy or starts medication to help control sexual arousal. Otherwise, it is meant to determine the likelihood of a person having sex offender tendencies. To calculate results, clinicians carefully consider the types of stimuli that caused reactions. Also, they look at the strength of the reactions, and they consider the factors that were outlined in the previous section in relation to this. In addition to other factors, they consider the length of time from viewing a stimulus to the time of the reaction.

As it is with most evaluations or tests, the PPG has the potential for errors. It is considered more reliable than a standard polygraph test in measuring the accuracy of the participant’s honesty in responses to questions. If a participant feels that the outcome of a test is inaccurate, showing reasonable cause to take it again may be possible. In such a case, it is helpful to consult with an attorney before seeking a second PPG test attempt.

Use in Criminal Defense

A variety of tests and evaluations may serve as valuable tools at different stages of a criminal case. In some instances, a person accused or under investigation may contact any attorney before an arrest is made. This provides an opportunity to communicate with the investigating detective or agent to provide information that may avoid a criminal charge being filed. If a case has been filed, but not yet indicted, then PPG and other results may be shared with a prosecutor for consideration at the grand jury in hopes of a “No Bill.” When a case is indicted and continues on to trial, then these kinds of tests may be a useful part of convincing a jury a person does not exhibit indications of pedophilia or hebephilia. In cases resulting in a conviction, the test may serve as mitigation at the sentencing phase (either judge or jury). When and how to use a penile plethysmograph can be a complex strategic and tactical decision.

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