Polygraph Lie Test
How it works
Phases of the test
Physiological parameters are monitored continuously with a polygraph instrument:
These variables produce sets of concurrent traces on the examiner’s computer screen, and at the point in time when any of the questions are answered by the subject a special marker is attached to the trace.
Two phases are involved in an appointment session:
Phase 1 comprises an interview. This typically is the longest part of the test and the time for it varies depending upon the reason for the test.
The purpose is for the examiner to fully understand the underlying issues at stake, to agree and define the specific wording of the questions to be answered, and then to calibrate the computer equipment so that the electronics are individualised.
The examiner will make precise automated baseline measurements of the physiological parameters listed above and this baseline will then be tested with a whole range of questions or issues or feelings held either strongly or weakly.
The testing involves a computerised analysis of the subject’s physiological reactions to these.
Phase 2 is the actual test which commonly lasts about 30 - 40 minutes.
The critical questions (called Relevant Questions) are agreed between the client and examinee in advance. They will always be asked at a minimum of 3 times - typically in different ways - and interspersed with other questions designed to maintain baseline reference.
The Relevant Questions are formulated once the key issues in the case have been examined. The number of these Relevant questions are typically 3 and in order to achieve the highest test accuracy, all 3 questions should ideally relate to one subject, i.e, a single issue. This is known as a Single Issue test.
The Relevant Questions are always known by the examinee in advance, and the examinee must agree to be asked these. The test is a completely voluntary process and nobody can be coerced into either doing a polygraph test or answering questions they do not want to.
All polygraph questions require a yes / no answer.
It is not possible to cheat the test, either by clever thinking, hypnosis, meditation or by drugs, because in order to do so a person would need to have conscious control of their heart rate, blood pressure, skin resistance and respiration rate - ALL AT THE SAME TIME.
Deception is indicated by characteristic changes in one or more of the 4 variables, immediately upon the subject’s response to a question and for a short period following.
Truthfulness (i.e. absence of deception) is shown by the absence of any such changes in these four continuously monitored variables, and will be visible to the examiner as no change in the trace pattern at that point, immediately as the subject answers the question, and also immediately afterwards.
The professional skill of the examiner rests in the precise way in which any question is worded, together with his / her experience of knowing what trace variations are significant – and what variations are not.
Do contact us if you have any questions.