Polygraph examinations: how do they work?

The physiological responses measured by a polygraph derive from the autonomous nervous system and, therefore, contradictory to certain “popular legends” amongst the public, they cannot be controlled and/or changed by the respondent in a polygraph examination. In contrast to another widespread belief, rather than being a machine that diagnoses the truth or a lie at the click of a button, a polygraph is a complex psycho-physiological process, which requires integration between a standard polygraph apparatus, a trained polygraph expert and a complete polygraph examination procedure, as detailed below.

The importance of a standardized polygraph apparatus and a qualified polygraph examiner with the appropriate training is obvious. However, many people tend to ignore the substantial importance of the polygraph examination procedure.

Prior to conducting a polygraph examination, on phrasing the questions to be examined, a professional polygraph examiner must obtain as detailed as possible background material for the examination. This background material will be of great assistance to the expert during the examination. Optimal phrasing of the examination questions is one of the most important components of a polygraph examination.

A standardized polygraph examination is conducted in a quiet room, sealed against external noises as much as possible. At the beginning of the examination, there is an introductory discussion, during which the respondent is asked questions aimed at receiving information on his/her mental and physical health situation in order to determine the degree of his/her suitability and competence to undergo a polygraph examination.

At this stage, a polygraph expert requests the respondent to present his full version of the subject of the examination and the reason as to why he came for an examination.

Now the examiner phrases the examination questions in the language and linguistics of the respondent together with the respondent.

The questions in a polygraph examination have to be as simple, clear and concise as possible. Questions with ambiguous answers should be avoided respondents in a polygraph examination have to answer the questions solely in the positive or negative. No questions, which the respondent refused to answer, should be asked. At this stage the respondents are connected to the polygraph apparatus and are asked agreed-upon questions a number of times, while recording their physiological responses to the questions on the polygraph apparatus.

At the end of the examination procedure, the polygraph expert analyzes the records. Certain physical logical responses, which are repeated a number of times regarding a specific question, will lead to the conclusion that the respondent was lying when responding to that question.