Polygraph Test

What is a polygraph test and how does it work?

In the world of criminal investigations and security clearance, the polygraph test has become an iconic symbol of truth-seeking and deception detection. Often depicted in movies and TV shows, the polygraph, or lie detector test, is a widely recognized tool.

But what exactly is a polygraph test, and how does it work? Let’s take a look at the intricacies of polygraphs, shedding light on its principles and applications.

What is a polygraph test?

A polygraph test, commonly known as a lie detector test, is a diagnostic procedure used to measure physiological responses that are believed to be associated with truthfulness or deception.

This test is based on the premise that when a person lies, their body undergoes subtle physiological changes that can be detected and recorded. The polygraph is designed to monitor and record several physiological indicators simultaneously, typically including:

  1. Heart Rate: The polygraph measures the subject’s heart rate or pulse rate.
  2. Respiration: It records the subject’s breathing patterns.
  3. Blood Pressure: Variations in blood pressure are monitored throughout the test.
  4. Skin Conductance: Sweat gland activity, as reflected in changes in skin conductance, is another key measurement.

How does a polygraph test work?

The underlying principle of a polygraph test is based on the idea that lying can cause stress or anxiety, which in turn results in detectable physiological changes. More specifically, when a person lies, their fight or flight response kicks in. Releasing adrenaline in your body which causes these physiological changes.

During the test, the individual being examined is asked a series of questions. These questions are categorized into three types:

  1. Relevant Questions: These pertain to the specific issue under investigation, such as a crime or incident.
  2. Irrelevant Questions: These are general questions that are not directly related to the issue but are designed to establish a baseline for the subject’s physiological responses.
  3. Comparison Questions: These questions are somewhat related to the relevant questions but are less specific. They serve to gauge the subject’s reaction to being deceptive.

As the subject answers these questions, the polygraph records physiological responses.

A trained polygraph examiner then analyzes the data to determine whether there were significant reactions, which might suggest deception or stress during certain answers.

RELATED: The meaning of crossed arms in body language.

Common myths about a polygraph.

1. Polygraphs can be beaten.

Some believe that individuals can easily manipulate the results of a polygraph test by using various techniques or tricks. While there have been cases of attempted countermeasures, skilled examiners are trained to detect such efforts.

2. Polygraphs are only about detecting lies.

While polygraphs are often associated with detecting deception, they can also be used in pre-employment screenings or security clearances to assess an individual’s honesty and integrity.

3. Polygraphs work equally for everyone.

There’s a myth that polygraphs are equally effective for all individuals regardless of their cultural or psychological background. In reality, different people may react differently to the test, and cultural factors can influence their physiological responses.

4. Polygraph results are immediate and definitive.

Some believe that polygraph results are available immediately after the test and provide a clear-cut answer.

In practice, the analysis of polygraph results requires the expertise of a trained examiner and may not yield a straightforward “lie” or “truth” determination. There are exceptions where an inconclusive result can be given.

Most examiners also tend to do “quality checks” on their scoring, meaning that they double check the results they have given, compile a report and only then can results be given to the client.

5. Polygraphs are admissible in all legal proceedings.

There is a misconception that polygraph results are universally accepted as evidence in legal proceedings.

The admissibility of polygraph results varies by jurisdiction, and many courts are cautious about admitting them due to their perceived unreliability due to examiner reliability.

6. Using medication can affect the polygraph.

The myth that medication can significantly influence the outcome of a polygraph test is a common misconception.

While some medications may affect physiological responses like heart rate or blood pressure, it’s essential to understand that polygraph examiners are trained to account for such factors.

RELATED: The 9 telltale signs of a pathological liar.

When would a polygraph test be used?

  1. Criminal Investigations: Companies use polygraphs to assist in investigations, as a tool to screen suspects or witnesses.
  2. Security Clearance: In some cases, individuals seeking security clearances for sensitive government positions are required to undergo polygraph examinations.
  3. Employee Screening: Some employers use polygraphs to screen potential employees.
  4. Periodical Screening: Most companies conduct polygraph tests on all of their staff over a set time period to ensure their integrity and honesty.
  5. Domestic Cases: A lot of people use polygraphs tests to find out information relating to personal matters such as a cheating spouse.


The polygraph test is a tool that has long fascinated and intrigued both the public and professionals in various fields. It is built on the premise that physiological changes can reveal deception.

As technology and our understanding of human physiology advance, we may see improvements in lie detection methods. In the meantime, the polygraph remains a complex and controversial tool in the quest for truth and justice.

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