Lie detection is not a new phenomenon. Way before the sophisticated equipment of today was introduced, we had our own ways of determining the honesty, or otherwise, of our fellow man, and the basis of those methods was surprisingly similar to the ones used now.

We know that when we tell a lie our bodies give us away – we start to sweat, our heart rate increases, and our breathing quickens. Ancient methods relied upon these responses as much as the modern day polygraph does, albeit in a much more primitive manner.

For instance, in the Middle Ages, infidelity by a wife would be determined by measuring her heart rate. A trained person would place a finger on the woman’s wrist while reciting the names of all the men she could be having an affair with. If her pulse rate increased at the mention of a particular name, not only was the wife found out, but also the lover.
African tribes had a unique (and far less pleasant) method of lie detection. A suspect would be made to stand, while a sorcerer would dance all around him, smelling his body. The stronger the body odour, the more likely the suspect was to be guilty, given that the body responds to lying by sweating.

Even centuries ago, our bodies responded to guilt. The methods might have changed, but our basic physiology has not, and it is these reactions which are the cornerstone of the modern day lie detector test.
There are several different questioning techniques used in a polygraph test today.

The Relevant/Irrelevant Technique (RIT)

One of the oldest methods of questioning, and perhaps one of the simplest, this method involves the examiner asking a set of questions which comprises of relevant questions, and irrelevant questions. A relevant question is one which relates specifically to the crime, or misdemeanour, being investigated.
For instance, if a 42-year-old man named John Doe from 123 Alphabet Street was being tested to ascertain whether or not he stole £5000 from his mother, the examiner might ask him a set of questions including:

  • Is your name John Doe?
  • Are you 48?
  • Do you live at 123 Alphabet Street?
  • Did you steal £5000 from your mother?

The first three questions are, obviously, irrelevant questions and are designed to provide a baseline reading for when the subject is telling the truth. They are easy to answer and should elicit no bodily responses. When he is then asked the relevant question of whether he stole the £5000 from his mother, if he is guilty but denies the crime, his responses will be markedly different from when he (truthfully) answered the irrelevant questions. If John Doe is, indeed, innocent, his reactions to the relevant questions would not differ from the irrelevant questions.

The Control Question Test (CQT)

Sometimes also known as the Comparison Question Test, this is a more widely used method of questioning utilised in polygraph testing. It is similar in style to the RIT shown above, in that there are two types of questions used. The examiner will ask relevant questions, as above, but also – instead of asking irrelevant questions – he will ask control questions, which will be indirectly relating to the misdemeanour or crime. So, assuming the same subject is under scrutiny, the questions might be:

  • Have you ever stolen anything?
  • Have you ever stolen money from a family member?
  • Did you steal £5000 from your mother?

Now, nobody wants to admit that they have ever stolen anything, but the chances are they have, even if it was a single sweet from the corner shop when they were five! But most times people will deny it because they will feel that under polygraph conditions, it will somehow make them look more likely to have committed the theft of the £5000, even if they haven’t.
The interesting part of this method is that an innocent person will react more strongly to the control questions, which they will probably be lying about, than the relevant question which they will be answering truthfully.
A guilty subject, on the other hand, will show a stronger reading when answering the relevant question, even though they will be lying on both the relevant and control questions. You might expect them to show a similar reaction to all of them – after all, they are being deceitful on every question – but the relevant question will provoke the strongest reaction because it presents a more immediate threat.

The Guilty Knowledge Test

The Guilty Knowledge Test (GKT) works in a different way to the previous methods. Instead of asking direct questions, such as “Did you kill Harry Doe, your brother?” the examiner will ask a multiple choice type question, instead.
To illustrate this further, let’s suppose that poor, hapless Harry died when his brother John (the subject) drowned him in the lake. In the Guilty Knowledge Test, John would be asked questions such as:

  • Was Harry stabbed to death?
  • Was Harry strangled?
  • Was Harry shot to death?
  • Was Harry drowned?

John is going to deny that he killed his brother, and as he is asked about each possible manner of death his reactions will be recorded. With the GKT it is assumed that John’s reactions will increase when he is asked “Was Harry drowned?” because that is the one question John will be lying about when he answers in the negative.

The Directed Lie Test

Lastly, a method sometimes used in a polygraph setting is that of the Directed Lie Test (DLT). The difference between this and the previous methods is that the subjects will be told to lie in response to the control questions, and while they are answering, to think about the times in their life when they did what they have been told to deny. The questions will cover a deliberately long period of time – often the subject’s entire lifetime – because the chances are that they, at some point in their lives, will have done exactly what they are being told to deny.

Confused? Ok, let’s look at this in further detail. Going back to our example in the CQT control questions, the examiner might ask “Have you ever stolen anything?” but this time the subject is being told to lie, and the question will be expanded upon by adding “during your entire lifetime?” Having already been told to think about the question beforehand, that single sweet from the corner shop when they were 5 is going to be playing on their mind and will show in their reactions. Their bodily responses to the relevant question will be much lower in an innocent subject.

However, a guilty subject will show a much stronger reaction to the relevant question than to the control questions, even though he will be lying on all of them – again, this is down to the immediate threat posed by the relevant question.

Single Issue vs Multi Issue Testing

This is not a method of questioning as such – any of the techniques mentioned could use Single or Multi Issue questions so it is more a variation on a theme, but it is an important factor in the success, or otherwise, of polygraph testing, which is why we have included it here.

Looking at Multi Issue Testing first – this is when an examiner asks the subject questions on several different issues during one session. Now, a client might think this offers much greater value for money if there is more than one issue in question. After all, why pay for several sessions when you can cover all bases in one, right?

Wrong! Although it might seem like a better idea, Multi Issue testing does not give accurate results. The focus needs to be on one issue, and one issue alone. Introduce another issue and you are merely muddying the waters. The subject will likely be flustered and confused, and the accuracy is compromised. Without getting too technical, the results of a Multi Issue test are far more open to interpretation, and therefore not reliable.

The Single Issue Test, on the other hand, will ask about only ONE issue. This keeps the test, and results, clear and concise and much more reliable and accurate. We only offer Single Issue Testing, because we want to give you the most accurate results possible.

The methods chosen will depend on several factors; the preferred method of the examiner, for example, and the nature of the crime or misdemeanour. Obviously extreme examples have been used in this article, but a polygraph test can be used to cover all manner of situations.

At the end of the day, whatever method of questioning the examiner employs, it all comes to what those African tribes and those suspicious husbands in the Middle Ages knew all along – our responses don’t lie, even when we do!