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The True Problem with Lie Detectors

About The Author

Edmund Day (Former Writer)

Edmund is a 3rd year student of Law with French at the University of Birmingham, currently studying towards the Certificat de Droit Français during his year abroad at l'Université Montesquieu - Bordeaux IV. Edmund aspires to be a solicitor, with a particular interest in the aviation sector.

Polygraph tests, also known as lie detectors, are soon to be trialled in the UK.  They will be used in risk assessments of sex offenders under the jurisdiction of South Yorkshire Police.  The technology will only be used to assess the risk posed to the public by offenders either on bail or being dealt with by probation, but these developments raise questions over the legitimacy of polygraph evidence and whether one day such evidence will be admissible in UK courts.

Polygraphs measure the physiological reactions of subjects, such as pulse, respiration rate, blood pressure and perspiration.  Although their official use in the UK is somewhat novel, they are found far more widely in the US.  Intelligence and law enforcement agencies, as well as Steve Wilkos (America's answer to Jeremy Kyle) all commonly use the technology.  Unsurprisingly, the key arguments over their use and credibility hinge on the core issue of reliability.

Shaun Wright, Police and Crime Commissioner for South Yorkshire cited the protection of the most vulnerable in society as the motive for the step.  He downplayed any heightened risk to the public, pointing to the fact that 75% of offenders who were subject to a 2011 trial by Hertfordshire Police had their risk level increased.

However, uncertainty remains over the reliability of polygraph results.  Developed and first used in 1921, critics argue that polygraph technology has still not evolved sufficiently to provide any valuable information.  The lingering doubts over the technology mean that lie detectors pose more questions than they answer, they claim.

Other than brief trials, polygraph evidence is yet to materialise as a feature of the UK legal system.  But as recently as last year, the Scottish system hinted at a review of the current situation in relation to polygraph evidence after a convicted killer posted a video online of himself passing a polygraph test, supposedly proving his innocence.  The case is now with the Scottish Criminal Cases Review Commission, the body responsible for re-examining cases to consider the need for appeal, retrial and the potential declaration of a miscarriage of justice.

As previously mentioned, polygraph tests are far more common in the US, which provides us with a convenient example for examination.  Across the Atlantic, Customs and Border Protection alone carry out over 10,000 polygraph tests each year.  They maintain that the technique annually uncovers 200 wrongdoers; a success unparalleled by any viable alternative technique.  But here, polygraph tests are used simply as the basis for further investigation rather than to form the basis of criminal evidence.  When it comes to the admissibility in court of such evidence, it seems that the doubts are simply too significant to authorise its use.  In 2013, a US man was jailed for eight months for coaching others how to deceive the machines.  Amazingly, this involved techniques as simple as controlled breathing, muscle tensing, mental arithmetic and tongue biting.  Even more amazingly, using these techniques his clients succeeded in skewing polygraph results in their favour.

Despite the apparent ease of fooling what appears to be somewhat archaic technology, the US Supreme Court continues to grant individual states the discretion to determine to what extent polygraph evidence is to be admissible in court.  Some, including New York State, Texas and Illinois decline its use all together.  Other states conditionally allow such evidence, either in relation to certain proceedings or dependant on the agreement of the parties, as is the case in California, Nevada and Florida among others.

It is questionable though whether this is an issue that should ever filter down to decision-makers at State level.  With some experts estimating the accuracy of polygraph equipment at just 65% (marginally superior to the 50% obtained by flipping a coin), the US Supreme Court moved in 1998 to restrict the use of polygraph evidence by barring its submission in court to prove a defendant's innocence.  This demonstration of a glaring lack of faith in the system raises concerns over why it is admissible in any capacity.  Even when juries are warned of potential inaccuracies, the sole outcome is likely to be further confusion.  It is unhelpful to add additional information into the mix, only to warn jurors that this information may be completely misleading.

The predominant obstacle preventing polygraph evidence from being of real use in ensuring fair outcomes within any legal scenario is that polygraphs do not measure honesty itself.  Instead, they measure arousal.  The previously mentioned physiological responses that a polygraph detects and measures respond to arousal, not necessarily honesty.  Whilst the ease of out-smarting a polygraph presents one issue, the matter of being wrongly disbelieved presents another.  Few people would fail to feel even the slightest sentiment of nervousness when being subjected to police questioning. Therefore, it is unsurprising that the responses supposedly consistent with dishonesty wrongly emerge with startling frequency under these conditions of heightened emotion.

In essence, no questioning technique based on this type of technology will ever boast 100% accuracy.  The simple fact that people differ on an individual basis means that the blanket solution the polygraph purports to provide will never be effective in all eventualities.  Even supporters of polygraph testing have conceded that an individual's questionable moral compass can detract from the production of reliable results.  What one man considers dishonest may not resonate as wrong with another individual, underlining the subjective nature of the techniques the polygraph relies on.

The use of polygraph testing can indeed identify every lie, in the same way that we are able to convict every criminal.  This comes necessarily at the cost, however, of convicting numerous innocent suspects, reflecting the attitude that it is preferable to sacrifice an innocent individual's rights than to risk a guilty individual escaping conviction.  So the polygraph currently fails to offer us any kind of step in the right direction.  If anything, it risks forcing us into a backward step.  Supporting its use is the thinking that any given suspect is more likely to be induced into telling the truth if they believe that they will be otherwise found to be answering dishonestly.  However, even this loose argument is undermined by the established questions and doubts surrounding the reliability of lie detector results.

When the US Supreme Court sought to limit the application of polygraph evidence back in 1998, it declared that “there is simply no consensus that polygraph evidence is reliable.”  This told us little we did not already know, but the acknowledgement of the sole dissenting judge, Justice John Paul Stevens, that polygraph results were accurate to a mere 70% spoke greater volumes.  One professor and polygraph researcher at Brandeis University, Leonard Saxe revealed why this figure will never reach the level of certainty required in legal proceedings.  “Because of the nature of deception, there is no good way to validate the test for making judgments about criminal behaviour. There is no unique physiological reaction to deception,” he explained.

Even if we are generous, and concede the 95% accuracy some polygraph supporters allege, this figure nevertheless falls short of the standard of proof in criminal proceedings.  It is certainly tricky to assign a numerical figure to represent exactly what 'beyond reasonable doubt' represents, but in any case 95% is unlikely to cut it.  'Beyond reasonable doubt' lies closer to absolute certainty than to 95%, so even at optimum performance, it is contentious as to whether polygraph evidence would meet the required standard.

In spite of this, polygraph evidence may be of use in civil proceedings where the standard of proof is much lower at 50%, based on the balance of probabilities.  Here the numbers play in its favour and suggest that it is more likely than not to facilitate investigators, prosecutors, and jurors in establishing the likely sequence of events in relation to any given suspect.

A useful tool in civil proceedings?  Probably.  A useful tool in criminal proceedings?  Certainly not.

Given current technology in the field, polygraphs will struggle to establish themselves as sufficiently reliable sources of evidence and fail to bolster the case for their use in criminal convictions.  For this reason, and in the absence of any miracle technological development, do not expect to see them appear in UK criminal proceedings any time soon.

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Tagged: Criminal Law

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