Professor of psychology Chris French writes for the Guardian on why mandatory polygraph screening of convicted sex offenders is a bad public policy choice. Excerpt:
It is clear that offenders only have to spend five minutes on Google to realise that experts generally agree that polygraph testing is in fact not a reliable technique for detecting deception. If such testing becomes mandatory, it is inevitable that this truth about polygraphs will become widely known among offenders. From then on, any effect that unfounded belief in the effectiveness of the technique had in terms of increasing disclosures is likely to disappear.
To make matters worse, techniques exist to beat the test. Once the underlying rationale of the test is understood, steps can be taken to either augment the psychophysiological response to control questions (eg via self-induced physical or mental pain) or else reduce the response to relevant questions (eg using mental training, such as meditation).