Lying is an inseparable part of human behavior, especially when a person does something wrong and does not want to be caught. The culprits of any criminal offense always try to avoid conviction by telling lies or framing false stories in front of the investigator. For an experienced investigator, it is easy to catch the lies of the suspect but in some cases where the hardcore criminals are so stubborn and insolent that they lie with a lot of confidence which is difficult to detect.

However, there is a saying “A lie has no legs”, and it has been proven in every conviction in one or another means. There have been various methods used by different cultures to detect lies in the earlier periods. But now with the new discoveries and inventions in technologies, a new method for detecting lies using the machine was developed which is now known as Polygraph.

Polygraph is a process or procedure of lie detection based on the study of the functioning of different body systems which is conducted on a person to detect lies. It is also known as a lie detector which measures the physiological responses of a person when they are questioned. There were many inventors of polygraph machines but the most common one in use was invented by John Keeler.

The principle of the polygraph is based on the fact that a person can deceive another person but not oneself. When a person lies, a mixture of emotions including fear and anxiety is produced which stimulates the sympathetic nervous system that causes physiological changes. These changes are recorded which can be indicative of deception. A person having expertise in reading the polygraph can interpret the results.

The important physiological changes that are considered for the study are:

  • Skin reaction
  • Blood pressure
  • Respiration rate 
  • Pulse 

The test carried out involves asking questions that are suggestive in nature and require answers in the form of ‘Yes’ or ‘No’. The difference in the above-mentioned physiological changes before and after the questioning indicates that the examinee may be deceptive.

Before conducting the polygraph examination consent of the examinee for the commencement of the test should be taken.

Components of Polygraph Machine

  • ChairThe examinee is asked to sit on the chair comfortably
  • Arm CuffIt is placed around the arm of the examinee and measures the blood pressure and pulse.
  • Belt A belt is wound around the chest of the examinee which records the respiration rate.
  • ElectrodeAn electrode connection is attached to the tip of the index finger for recording the galvanic skin reaction.

When these connections are made on the body of the examinee, the questions are asked of him. Usually, 8-10 questions are asked of the examinee. The responses of the concerned physiological process are recorded on a single paper which is analyzed by a polygraph expert.

Types of Questions Asked 

The results of the polygraph are interpreted by the responses achieved depending on the nature of the questions asked by the examinee. The following types of questions asked are:

  • Relevant Questions: These are the questions that concern the incidents related to the offense.
  • Irrelevant Questions: These are the questions that do not relate to the incidents.
  • Control Questions: They are also known as comparison questions because they compare responses to relevant questions with responses to other questions that are intended to generate physiological reactions even in non-deceptive examinees.

It determines the level of truthfulness which varies in genuine and deceptive examinees. In the genuine examinee, the level of truthfulness is quite high without any anxiety, whereas in the deceptive examinee, the truthfulness level is low and it is presumed that the relevant questions create a greater level of concern and therefore a stronger physiological response.

How Polygraph Test is Conducted?

A pretest interview is conducted on the examinee before the polygraph examination. In this interview, the examinee is told about the examination process, what type of questions will be asked in the test and what is the need for the test.

The purpose of the pretest interview is to shape the emotional state and expectations of the examinee during the test. The examinee is convinced that the machine can detect every lie. The examinee is asked to tell a lie deliberately which is detected by the machine and makes him/her believe the reliability of the machine.

This demonstration is also termed as ‘stim test’. Sometimes this is used to deceive the examinee so that he/she does not try to lie during the polygraph examination. 

After the commencement of the pretest interview polygraph examination is conducted and a combined graphical result of the response is formed by the examiner. So it can be said that a polygraph examination is a consolidated impression of the interview or interrogation technique and a psycho-physiological measurement or testing technique.

Usually, a polygraph examination is used by investigating agencies to examine deceptive criminals. However, in countries like the United States, Israel, Japan, and Canada, the polygraph is used in pre-employment screenings in law enforcement agencies. It is also used in screening the employees of security agencies.

Controversies Related to Polygraph

The results of the polygraph examination are inadmissible in court because it has a high percentage of false positivity.

In 1923, in Frye vs The United States, the District of Columbia Court rejected the scientific validity of the polygraph because the technology did not have significant acceptance at that time. This was the incident that made the courts think about making the decision on accepting any kind of scientific evidence.

In India, the first case when the court adopted the results of polygraph took place in 2008 when a woman was convicted of murdering her fiance. However, in 2010, the Supreme court of India declared the use of the polygraph, narco analysis, and brain mapping on the suspects as illegal if the examinee does not give consent.

In fact, it is mentioned in Article 20(3) of the Indian Constitution which states that “No person accused of any offense shall be compelled to be a witness against himself“. However, the polygraph test is legal in India if the defendant requests it.


The polygraph examination is a psycho-physiological test that helps to reveal the deception of a person. Although the positive results have a percentage of about 87-90 percent, the false positivity rate is also high which limits its admissibility in courts. However, it can be accepted by the court if both parties related to the case agree to the conduction of the examination. 

The polygraph test is a useful method of lie detection but has certain limitations which need to be worked upon so that it becomes acceptable in courts without any controversy.

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Frequently Asked Questions

1. Are Polygraph Tests Accurate?

Scientific studies suggest that a polygraph is an accurate method of about 80-90%. According to them, they are imperfect and invalid means of questioning truthfulness. These tests do not tell if a person is actually lying but measures levels of fear and physical responses.

2. Can a Truthful & Innocent Person Fail a Polygraph Test?

Yes, a person can fail a polygraph test since they detect the lie using the anxiety levels of a person using the machine. Due to these reasons, a polygraph is an unreliable method and many people have failed them.

3. What is The Difference Between a Polygraph & Narco-Analysis?

Polygraph test relies on the physiological indicators of a subject whereas Narco-analysis uses drugs to change the subject’s change of awareness. Both of these techniques do not have a 100% success rate.

Categories: Criminology


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