In This Section:

Polygraph Testing

The key to accuracy in polygraph testing lies in the quality of the examiners.

In fact, the most important part of the test - which typically lasts two or three hours - is the preparation stage.

A polygraph test simultaneously records changes in blood pressure, heart beat, pulse rate, muscle movement, and perspiration and respiration levels.

Used as a lie detector by investigators and crime enforcement officers more than ever in Australia, it is increasingly being employed to pre-screen candidates for sensitive assignments or to test for substance abuse.

Accuracy

With accuracy rates of up to 95%, some believe that only sociopaths, psychopaths, or simply incredibly good liars who can tell a lie "honestly" will slip through the polygraph net. Inconclusive tests are very rare indeed. However, while polygraph tests are seen as indicators of honesty (or otherwise), results are always used in conjunction with strong supporting evidence.

The Process

The examiner first endeavours to put the interviewee at ease, and will then ask a series of questions to which the answer is known. The recorded responses to these questions act as a baseline for the interrogation that follows.

Examinations are totally painless, with the interviewee hooked up to two pneumograph tubes - one attached to the upper chest, and the other to the abdomen. In addition, metal plates are attached to the ring and index fingers, and a blood pressure cuff is wrapped around the upper arm.

Integrity of Testing

To maintain the integrity of the test it is important that the examinee is honest about bothersome questions so that the examiner can avoid triggering unnecessary stress responses.

For example, if asked about drinking habits, it's perfectly plausible for an examinee who is only a social drinker to become nervous if his or her parents were habitual drunks and the question triggers bad memories.