The dubious junk science behind the Domestic Abuse Bill

The government wants to use lie detectors – a discredited pseudoscience – to determine whether domestic abusers are telling the truth.  

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In crime and law enforcement, truth is the Holy Grail. The justice system is established to determine fact from fiction, and to judge the credibility of statements from witnesses, victims and defendants. But it’s a system that is prone to bias. Lawyers can draw on sexist cultural stereotypes to manipulate juries; judges can be racist, declare victims responsible for their own rape, or state that abusive husbands are otherwise ‘good men’. A device or system that could accurately determine if someone is telling the truth has the potential to transform the justice system.

Enter the polygraph test. Commonly known as a lie detector, polygraph tests have been popularised by the Jeremy Kyle Show, which uses lie detectors for dramatic effect to ‘prove’ whether a hapless partner is cheating. The show also makes use of paternity tests – a legitimate instrument that unwittingly lends credibility to the polygraph’s junk science.

Despite the lie detector’s dubious nature, the government wants to introduce polygraph tests for offenders convicted of domestic abuse-related crimes as part of the forthcoming Domestic Abuse Bill. The draft bill, published earlier this month, casually recommends that the national probation service will “pilot polygraph testing with high risk domestic abuse perpetrators”, as a condition for offenders' release on license. Polygraph testing is already in use; the 2007 Offender Management Act instigated polygraph tests to manage sexual offenders released on licence. The Domestic Abuse Bill proposes extending the use of this technology to assess the risk of a domestic abuser reoffending.

It’s unsurprising that law enforcement might look to science for objective measures of truth-telling. But there is no device that can accurately show if someone is lying. The technology simply doesn’t exist. Nothing, and no-one, can read minds. The only way to tell fact from fiction is through hard evidence. Somebody who claims they weren’t at a crime scene can be exposed through CCTV footage showing the contrary. Unless the person admits they were lying, the act of lying is extremely difficult to prove – the best that law enforcers can do is find evidence that contradicts a person's statement.

Polygraphs belong firmly in the realm of ‘pseudoscience’ – something that sounds legitimate but lacks the rigorous, objective standards of evidence that we expect from actual science. Those who manufacture polygraphs disagree (as they would), but there is a scientific consensus that polygraphs – which purport to measure emotional responses to questions – are not a consistent or reliable way of ascertaining truth.

That pseudoscience is already used to monitor sexual offenders is a staggering fact. Polygraph tests aren’t admissible evidence precisely because they are so subjective; it’s easy to Google how to fool a polygraph, and the results are often wrong because of confounding factors such as heart rate.

Crime detection has long courted junk science, from Cesare Lombroso’s theory that criminals could be identified through physical characteristics – which led to the much reviled theory of phrenology – to the British Department of Transport’s body language programmes, which are still used today in airports. Once these things are debunked, they quickly become outmoded. Not polygraphs. 

Improvements to the way domestic violence is handled are badly needed, but using outdated, discredited technologies will put the public at risk. In the UK justice system there should be no space for the lie that is polygraph testing.

Tracy King is a freelance science writer and contributor to the New Statesman.