Forensic psychiatrist discusses if lie detector tests are reliable

Forensic psychiatrist reveals the truth about whether lie detector tests are accurate and reliable

  • Forensic psychiatrist Dr Sohom Das, London, discussed if lie detector tests work
  • READ MORE: Could YOU be conned? Psychiatrist reveals what factors influence the answer – including your personality traits and vulnerabilities

An expert has discussed whether or not polygraphs – also known as lie detector tests – are actually effective when it comes to detecting deception.

Dr Sohom Das, 44, is a forensic psychiatrist based in London. He is also a YouTube content creator, who runs a channel called A Psych for Sore Minds.

There, he covers a range of mental health and crime-related topics, as well as commentary on news and culture issues.

His YouTube biography describes him as a professional Consultant Forensic Psychiatrist and expert witness discussing his own real life (anonymised) cases. 

In addition, it says: ‘Dr Das (MBChB, BSc, MSc, MRCPsych) has ‘personally assessed hundreds of patients in prisons, secure locked psychiatric wards and courts across the UK.’

Are polygraph tests reliable? The general consensus is that they are not effective when it comes to deception detection (stock image)

In a recent video, titled Are polygraph tests accurate or reliable enough?, he discusses the devices.

Some people and organisations state that polygraph tests can have a very high accuracy rate when it comes to showing whether someone is a liar.

However, polygraphs largely fell out of favour in the deception detection field in the early 2000s.

Polygraph tests measure fear-based arousal someone will show while answering crucial questions. 

These physiological markers include things like sweating.

The idea that these markers will change while lying is based on the premise that anxiety around deception increases due to the liar’s fear of being caught.

Speaking in his video, Dr Das explains this.

He says: ‘The main problem with the polygraph test is that they are not accurate and they only measure anxiety as opposed to measuring people actually lying.


The polygraph, the most common lie-detection instrument, works on the assumption that the body reacts involuntarily to the stress of lying.

It measures reactions such as changes in skin conductance, pulse rate, blood pressure, and breathing while the subject is asked a series of questions.

Using a number of sensors attached to the body, physiological changes can be used to determine whether someone is telling the truth.

A major change in any pattern, also known as a ‘response conflict’, is thought to be a sign a person is lying by some.

‘The polygraphy will measure biological processes to determine whether the subject is experiencing physiological events such as an increase in blood pressure, or an increase in heart rate.’

Researchers have said that this does not proves someone is lying because liars do not necessarily show greater signs of arousal when addressing these questions.

On top of that, people telling the truth may be anxious while answering questions, and therefore show increased arousal.

This therefore means that physiological changes are not necessarily a reliable marker of deception.

As a result, polygraph tests cannot be used as evidence.

They cannot be used either as evidence in criminal court or as the basis for recalling offenders to prison.

Dr Sohom Das (pictured) is a London-based forensic psychiatrist who also makes YouTube content on his channel A Psych for Sore Minds

However, the results of polgraphy tests may be used in civil courts at the discretion of the judge 

However, lie detector tests are sometimes used by law enforcement. 

Dr Das explains this in his video, saying: ‘They have been used to convince the perpetrator that they are completely accurate.

‘So, they pressurise the perpetrator into confessing, so the perpetrator thinks they have to tell the truth and admits to the crime.

Dr Sohom Das can be found on Twitter, Instagram, and TikTok, as well as YouTube.  

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