With a chequered history, polygraphs were quite famous in the fifties comic books and shows like Jeremy Kyle. With the rising criticism on the efficiency and effectiveness, law agencies in America still continue to use them. With this growing use, governments are now planning to adopt them in determining if rapist and paedophiles would be sent back to jail.


Ministry Of Justice

What this implies is that the Ministry of Justice would give the go ahead to probation officers to use polygraph on paroled sex offenders. If the test comes back negative for them, paroled sex offenders would find their way back to prison. This became more admissible after a study by the University of Kent was examined. The study showed that the probability of offenders clinically disclosing little information doubles when subjected to a polygraph test.


Ministry Of Work And Pensions

For a test that many experts have described as pseudo-science and flawed, the British law enforcement agencies are still continuing with the test. Polygraph machines are not just the only methods being considered finding offenders. Graphology (revealing personality through handwriting), mind reading MRIs, voice-stress analysis, etc. are other methods that have been applied. Their use have grown beyond the reaches of the police departments as voice analysis is now being used by the Ministry of Work and Pensions to investigate cases of cheats.

According to critics, the main reason for their opposition is the fact that it lacks concrete reliability, scientifically. Dr Sile Lane of the Charity Sense About Science speaks of the flaws on the methodology used when conducting polygraph tests. In her words,

“The researchers downplay the bias of the observer, which surely should be a large concern since the research depended on offender managers deciding what was or wasn’t a clinically significant disclosure”

If we are to go by this, when then are many policemen and even politicians still dedicatedly convinced of its usefulness? What really is the principle of the lie detector?


Control Question Technique (CQT)

Simply put, polygraph machines are unable to detect lies. The lie detector is only able to detect heart rate and physiological proxies. It functions on the principle of Control Question Technique (CQT). To begin the test, the private investigator would ask some “control questions”. Usually some of these questions relate to the investigation. A good example of a control question is, “have you ever told a lie to escape trouble?”.

It is generally believed by private investigators that someone who is guilty would show more stress when asked real questions on crime than when answering the control questions. On the other hand, an innocent person will appear stressed for both real and control questions. Indicators of deception used are an accelerated heart beat and physiological proxies.

According to Richard Wiseman, professor of the Public Understanding of Psychology at the University of Hertfordshire, although the tests are rare, it is possible to test the effectiveness of a polygraph test. Only when answers have been verified like in a polygraph test can one be able to ascertain if a person is lying or telling the truth. He further commented that “the polygraph seems to be very good at catching liars but it seems very likely to give false positives as well, to “catch” people who are telling the truth”.