Risk assessment and polygraph testing

Police policy makers have typically been both cautions and suspicious about the use of polygraph testing, but in 2014 two police forces began to use polygraphy as part of their management of registered sex offenders. Since then another 12 forces have taken it on, and it has become possible to attach a polygraph condition to Conditional Cautions and Sexual Harm Prevention Orders. Nearly 3,500 individuals have now been tested, and approximately 5,000 tests have been carried out by police examiners.

Our data shows that over three quarters of these tests have resulted in previously unknown information being disclosed, sometimes leading to arrest, and nearly all have contributed to offender supervision. A recent independent review of police led management of sex offenders in the community recommended that polygraph testing in this setting should be made available to all forces (Creedon, 2022).

A polygraph test both obtains information and validates it.

In view of the demonstrated contribution of polygraph testing to sex offender management it might be reasonable to ask about its potential for use in other contexts such as preemployment vetting, disciplinary proceedings, and Covert Human Intelligence Source (CHIS) oversight in order to not only detect problematic behaviour after it’s happened, but also to help prevent it from occurring in the first place. To some this perhaps sounds too ‘American’ (although polygraph is in fact used in these types of setting in a number of countries), to others too controversial. Discussion, however, tends to be hampered by a misunderstanding of how polygraphy works and how it is, and can be used, not helped by the way in which it is portrayed in movies and on television.

Polygraphy and deception

Before even considering whether polygraph testing can or should have a role in policing beyond the management of sex offenders, however, a number of points need to be made:

First, although the polygraph is often called a ‘lie detector’, it doesn’t detect lies. Instead, it records the physiological arousal associated with the cognitive processing required to lie, which involves memory, emotion, decision making, and inhibiting the default response of telling the truth, amongst other things. While cognitive arousal is of course not specific to lying, the way in which the polygraph examination is constructed aims to ensure that in this instance it is the deceptive response to a specific question that is the cause – this is achieved in a lengthy pre-test interview in which the salience of a small number of relevant questions is established which then become the focus of the test itself; the pre-test interview may take two hours or more while the testing phase lasts less than 15 minutes in total.

...although the polygraph is often called a ‘lie detector’, it doesn’t detect lies.

Second, while the polygraph is not 100% accurate in discerning deceptive from truthful responses, it performs much better than you or I can do on our own, with or without training (most studies find that training increases confidence but not accuracy) – best estimates are that a properly trained examiner using validated techniques is correct in 80 to 90% of cases compared with a 50 to 60% success rate for most individuals, even detectives (e.g., National Research Council, 2003). The 10 to 20% error rate, however, means that while the outcome of a polygraph test can be used to contribute to decision making, it is not relied upon on its own.

Third, there are two outputs from a polygraph examination, the test result itself (truthful or deceptive), and disclosures. They are complimentary to each other. A polygraph test both obtains information and validates it: since the start of police testing, disclosures of new information have been made in over 70% of tests with truthful outcomes, and in about 70% of tests following a deceptive outcome (although the latter are unlikely to be full disclosures, they open up useful lines of enquiry). Even without disclosures, however, the test result has meaning, with a truthful outcome providing reassurance and a deceptive one displaying a warning light that further investigation may be necessary.

Taking the above into account, the potential benefits of including polygraph testing in making decisions related to hiring, transfers into sensitive posts, disciplinary proceedings and accepting the account of a CHIS come into focus. Not only could it help avoid employing the wrong people or acting on incorrect information, but anecdotal evidence suggests that knowledge of an impending polygraph inhibits some inappropriate individuals from applying for posts in the first place, discourages those in post from engaging in problematic behaviour, and encourages honesty in CHIS (unfortunately this is not the type of matter that lends itself readily to a research study, and what data there is tends to be closely guarded by the agencies that hold it).

Objections

What then are the objections? The main concerns appear to be that polygraph testing is intrusive, there is a risk of overreliance on its results, it can be beat, and it may be used in inappropriate ways.

While all these issues need attention, they can be mitigated by a well designed and implemented testing programme. The questions asked during a polygraph test are no more intrusive than those already being asked, the only difference being that the individual is put on notice regarding deception; all techniques used by the police have error rates, and it is not clear why polygraphy should be signalled out as the one whose results will override all other considerations (and there is nothing to indicate this is happening in sex offender testing); the polygraph can indeed be ‘beat’, but it takes practice to do so, and the few who might ‘beat’ it are already beating the system anyway, while many more who otherwise do so will be caught; and inappropriate use can be prevented by a proper quality control programme.

While the arguments for incorporating polygraph testing in a range of procedures beyond sex offender management are not cut and dried, there is now experience and data stretching over a number of years regarding the impact of polygraph testing in a police environment. There is also a considerable amount of evidence relating to polygraph testing of domestic abuse and terrorist offenders in addition to sex offenders by the probation service. Decisions about whether it should be put to wider use no longer need be based on what happens on daytime television.