Lesson 2 - The Polygraph Examination

Page 2

Phases of the Exam II
 

2.  Questioning Procedure

The questioning procedure phase of the polygraph examination lasts no longer than a few minutes. The examiner allows the subject about 10 seconds to answer a control question; 15 to 20 seconds are given to respond to a relevant question. Each question may be repeated three or four times. During this phase of the exam, the polygraph examiner stresses to the subject that he or she must answer the questions with a simple "yes" or "no".

In a questioning procedure that involves CQT, the control questions asked focus upon behaviours that are similar to the crime being investigated.   They are vague questions that are related to a behaviour that many people may have committed or have considered committing. An example of a control question is  "Have you ever lost your temper and caused some type of harm to someone?"

Photo courtesy of Sergeant A. Kowalyk, 2005.

Answers to the control questions are meant either to be deceptive or to show concern about the responses. Control questions cause more stress in an innocent subject who is being truthful. The deceptive subject exhibits more stress to the relevant questions. The polygraph examiner compares the responses given to control questions and responses given to relevant questions to determine if a subject is being deceptive.  If a subject shows stress in his or her answers to relevant questions, the polygraph examiner pursues this line of questioning because this means that the subject is likely being deceptive and knows more than he or she is saying.

During the CQT, that a subject not be able to distinguish between the relevant and control questions is important. If the subject knows which questions are more important for the score, he or she may make anticipatory responses that could alter the results.

3.  Post-test Interview and Analysis

During the post-test interview, the polygraph examiner collects and compiles the physiological data recorded by the polygraph instrument with each answer given by the subject. The polygraph examiner may briefly review and analyze some of the data while the subject is still present.  This initial review may lead to the subject being asked to explain any response or reaction to specific questions of interest to the polygraph examiner.

The physiological data collected by the polygraph instrument includes the heart rate, blood pressure readings, the breathing rate, and perspiration rate. After analyzing the data related to each answer, the polygraph examiner gives each answer a score using a numerical scoring system.  Scores are based on which questions cause the subject the most stress and how much the responses to the relevant questions and the control questions deviate from one another.  Conclusions regarding the validity of the exam are made according to the number of deviations and the magnitude of the deviations.  Visual observations of the subject under interrogation made by the polygraph examiner are also used.  In general, a significant change (for example, faster heart rate, higher blood pressure, increased perspiration) indicates the subject is lying.

The polygraph examiner makes one of the following three conclusions at the end of the post-test interview and analysis: 

  • the subject was truthful
  • the subject was deceptive
  • the results were inconclusive

Did you know?

"Why would anyone lie?  The truth is always more colorful."

- James Hall

"No man has a good enough memory to make a successful liar.

- Abraham Lincoln