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Polygraph Lie Detector FAQ
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What happens in a polygraph examination?
A polygraph examination consists of:
- a pretest interview,
- the collection of charts
- an analysis of the polygraph chart
- consultation with appropriate persons.
The average polygraph test will usually last 2-3 hours from, beginning to end. Most people don't realize the longest part of the examination will be the 45-90 minute "pretest interview." During the pretest interview, the examiner will:
- give detailed instructions for the actual testing phase, and confirm the examinees understanding of these
- define the subjects legal rights
- explain the polygraph equipment and how it works
- discuss at length the "issue" (for private issues, such as infidelity, both parties may be present during the discussion portion of the test)
- review all questions to be asked during the actual polygraph examination
To conduct actual examination, the examiner will attach the components to the examinee. These are totally painless, but they are very stressfull. They consist of:
- two pneumograph tubes are attached across the upper chest and abdomen,
- two metal plates are attached on the ring and index finger,
- and a blood pressure cuff is attached around the upper arm.
During the actual examination the collection of charts (polygrams), the examiner will ask the questions which were previously reviewed, three to four times. The examiner will conduct three to four separate charts before rendering an opinion.
Regardless of what you see on TV, a real polygraph is given in private. Although the process is often audio and/or video taped, only the examiner and the examinee are in the room.
After the collection of charts are concluded the polygrams are scored by computer using an algorithm developed by the Applied Physics Laboratory, of Johns Hopkins University. The charts are also numerically scored by the examiner. If further questions exist after the scoring is concluded, the examiner will seek a second opinion.