How Credible Is A Polygraph Test?

Polygraph test, commonly known as lie detector test is the scientific way of detecting deception through the use of a polygraph instrument. If carried out by a Forensic Psycho-physiologist (i.e. a qualified polygraph examiner), research shows that polygraph test is more accurate in finding out the truth than the most commonly known means including eye witness and fingerprints!

Although very popular and adopted in almost all the developed countries, the significance of the polygraph practice in quest for the truth is gradually making it the norm in various African countries including Nigeria.  

Polygraph instrument records the subject’s involuntary reactions to questions asked by the polygraph examiner in an ongoing investigation to detect deception. During a polygraph test, several indices like the blood pressure, pulse, respiration and skin conducts are gathered and analysed.

The first modern polygraph instrument was created by California based policeman and physiologist, John A. Larson in 1921. He devised an apparatus to simultaneously measure continuous changes in the blood pressure, heart rate, respiration rate and perspiration to detect deception.

While a subject’s nervousness is not an indication of guilt and does not have any bearing on the outcome of the polygraph test, it is believed that lying is accompanied by an increase in blood pressure which is measured by a cardiograph; an increase in heart rate which is measured by the pneumograph; and an increase in perspiration which is measured by the electro-dermal activity plates. Lower body movement is also measured by the seat sensor during a polygraph test.

The question that begs for an answer is, how reliable is polygraph?

Based on extensive research and as published in the forensic science report journal, polygraph is about 95% accurate when conducted by a competent and certified polygraph examiner. Research shows that polygraph is more accurate than fingerprint, eye witness, voice stress etc. Aside the competency of the examiner, other factors that can affect the outcome/ accuracy of the polygraph are: proper comprehension of the case facts, type of formats and scoring methods used, functionality of the instrument, condition of the testing room or location, psychological set on the part of the examinee and question formulation.

A typical polygraph examination comprises three phases which are: the pre-test phase, the in-test phase and the post-test phase. For any polygraph test to be valid a consent form must be signed by the subject shortly after the commencement of the pre-test phase while a consent release form must be signed after the post-test phase.   

Situations where polygraph test are used are:

  • In cases involving law suits and criminal trials, polygraph can be used as a tool to bolster evidence and encourage trustworthiness of a witness.
  • Polygraph can be used to help security agents and firms in investigations.
  • A lot of organizations use pre-employment polygraph test to screen applicants before employment especially if a sensitive position is involved.
  • Periodic polygraph test is the type of test carried out on current employees to prevent fraudulent activities.  
  • Banks and financial institutions use polygraph to determine employees’ honesty in an internal investigation when the need arises.
  • Commercial theft/fraud investigation also requires the use of a polygraph test.
  • Polygraph test also helps in infidelity cases. 

Hogan Polygraph & Investigations is one of only a handful of companies in Nigeria offering polygraph services. Contact us today for more info!

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