The lie detector operates by recording the changes in a person’s heart rate, breathing and perspiration during questioning. These changes are recorded by the computerised polygraph in a chart format which can then be analysed by the examiner. The chart is generated through several components:
Pneumograph – Two tubes are placed around the upper chest and abdomen on the outside of the person’s clothing. These record changes in respiration.
Galvanic Skin Response – The galvanic skin response (or GSR) is recorded by two attachments placed across the fingers on one hand. These trace changes in skin perspiration during examination.
Cardiosphygmograph – This traces changes to blood pressure and pulse rate and is similar to the pressure cuff used by doctors when taking blood pressure.
About the lie detector test
The lie detector test takes between 2 to 3 hours and consists of three phases:
A pre-test interview
The actual lie detector test
Analysis of the recorded response charts
Pre-test interview and formulation of questions
During the pre-test interview, the examiner will explain how the lie detector test works and discuss the issue in question with the subject. Together they will agree and review the questions to be asked during the test, and only these will be asked. The subject can be confident that there will be no surprise questions during the lie detector test as they have had the opportunity to discuss them in detail before the test begins.
Analysis of the results
Once the examination is finished, the examiner will analyse the results before giving a decision about the subject’s truthfulness or deception to the given issue.
How reliable is lie detector testing?
The polygraph is highly reliable, provided the person using it is properly trained and the technique they use is validated. The American Polygraph Association (APA) has conducted studies which show the reliability of the tests to be as high as 98%. The critical issue here is that the examiner has graduated from the APA training school, that they are experienced, have undergone continual professional development and the results are quality controlled by a qualified instructor.
“I hired a meeting room in Newcastle and was met by an extremely knowledgeable, friendly and patient examiner. He explained the procedures and processes involved in great depth and answered all the questions I had regarding the test. The test itself was performed 3 times for accurate results and gave me the answers I expected straight away with a full report being emailed that evening. Can’t recommend highly enough and would use the service again if need be.” – Happy customer
For professional lie detector testing
contact the experts at Polygraph International UK in the West Midlands on