A lie detector test, also known as polygraph testing, is becoming a popular method of proving innocence and finding out the truth in the UK today. Although there is widespread criticism of the techniques used in polygraph testing, the credibility of the test itself is still high, given the modern methods and new uniformity regarding the testing system used in lie detector tests.

The main aim of a lie detector test is to find out if the person being tested speaks the truth or not. The test doesn’t read what’s on the person’s mind; it detects changes in the person’s physiological responses as a result of answering questions given to him during the test.

Since polygraph testing is all about questions, answers, and physiological responses, many people ask what exactly is the mode of questioning done during these tests. This article will cover two of the common questioning techniques examiners utilise during a polygraph test.

The Control Question Test Technique

Traditional polygraph examiners use a technique called Control Question Test (CQT) to determine the questions to be asked in a polygraph test. The Control Question Test is widely used in cases involving criminal investigations, but may also be used for other polygraph test cases.

Questions under the Control Question Test technique are divided into two categories, control questions and relevant questions.

Control questions are broad questions related to the case matter, but are asked to make the person concerned about their past truthfulness and credibility. Examples of control questions may include the following:

  • Have you ever lied to anybody before?
  • Did you ever try to inflict harm on a woman before?
  • Have you ever tried to betray a person who trusts you completely?

Some control questions regarding the examinee’s identity and perception may also be asked. These questions are similar to the following examples:

  • Is your name really Joe?
  • Were you born in 1975?
  • Are you 47 years old?
  • Is today Friday?

Relevant questions are asked with respect to the direct case itself. These questions are often answerable by yes and no, just like the control questions. Here are some examples of relevant questions:

  • On 25th May 2016, did you shoot John Williams?
  • Did you steal £700 from the cash register?
  • Have you contacted a drug dealer last 15th of June 2017?

How Control Question Test Works

A truthful examinee gets more physiologically aroused when asked a control question, since these questions imply a casted doubt about his overall credibility. When a truthful person answers a relevant question, he is less aroused because he knows that his answers are not a lie. A higher response to control questions leads to a reading of “non-deception”.

An examinee who fabricates his answers for both the control question and the relevant question will both register high physiological responses. However, when he lies about his answers on the relevant questions, the polygraph may record an even higher response than when he answers the control questions. This leads to a reading of “deception”.

The Guilty Knowledge Test Technique

Polygraph science is now becoming more interested in the questioning technique known as the Guilty Knowledge Test (GKT). The test’s aim is to check the examinee’s guilt by using knowledge that only a guilty person will know.

In this test, the examinee is asked a series of multiple choice questions regarding the case. Here are examples of questions that may be asked under the GKT technique:

  • Did you steal £30, £300, or £3000?
  • Have you used a gun, a knife, or a blade in slashing your wife’s wrists?

A guilty person will recognize the correct choice in such questions, as he knows what happened to the crime or to the case. He can deny the fact that he stole money, or that he used a weapon. But he will likely recall the amount of money stolen or the weapon he used in inflicting harm on his wife. This is referred to as guilty knowledge.

A guilty examinee might try to hide his knowledge by answering an incorrect option. In these cases, the examinee will typically display a spike in physiological changes, indicative of deception.

Wrapping it Up

The two most common questioning techniques utilised by polygraph examiners include the Control Question Test and the Guilty Knowledge Test. Each technique has its own set of questioning methods that spark changes in physiological responses, leading to diagnosis of either deception or non-deception. These two have both been useful in successfully gleaning out the truth from various examinees in cases such as murder, theft, and fraud.