The polygraph examination, when conducted by a competent examiner, has up to a 95% accuracy rate. The polygraph instrument is the most reliable available method today to determine truth or deception, and scientific evidence supports the high validity of polygraph examinations. It is important to note that the validity of polygraph examinations requires a combination of a properly trained polygraph examiner and an instrument that records at a minimum cardiovascular, respiratory, and electrodermal activity. The word polygraph means many recordings, and to be considered valid, the aforementioned physiological activities must be recorded with the instrument simultaneously. It is for this reason that instruments that claim to detect voice stress have shown no scientific evidence of detecting truth or deception with any validity. It is also important for polygraph examiners to follow the format of the accepted structured test question techniques and proper scoring methods. Click here to view Truth vs Myth related to the accuracy of voice stress analysis.

There are also protective measures that are used to reduce any false conclusions by the examiner based upon the results of the examination. The methods are:

• The examiner conducts an assessment of the examinee's emotional state at the time of the examination
• The examiner gathers medical information about the examinee's physical condition
• Structured tests are conducted to identify the overly responsive examinee and to calm the overly nervous
• Comparison questions are used to evaluate the examinee's response capabilities
• All of the factual information about the issue to be resolved is thoroughly reviewed
• The examiner conducts a pre-test interview with the examinee
• All of the questions to be asked during the polygraph examination are reviewed with the examinee so that there are no surprise questions asked during the examination

The following information is from the American Polygraph Association’s web site, which is www.polygraph.org.

Scientific evidence supports the high validity of polygraph examinations, and examinations have great probative value and utility for various uses in the criminal justice system. The polygraph is not a “lie-detector” but rather an instrument used in conjunction with a clinical procedure designed to diagnostically determine truth or deception. A polygraph examination requires a combination of a properly trained examiner, a polygraph instrument that records at a minimum cardiovascular, respiratory, and electrodermal activity, and the proper administration of an accepted testing procedure and scoring system. As an analogy, the polygraph instrument can be compared to an x-ray instrument. Both the polygraph and x-ray instrument need a competent examiner to make a valid and reliable analysis of the results. With the improved instrumentation, namely the computerized polygraph instruments, and standardized testing procedures and scoring system, the polygraph examination is a very accurate means to determine truth or deception.

The American Polygraph Association has a compendium of research studies available on the validity and reliability of polygraph testing. Researchers conducted 12 studies of the validity of field examinations (real life), following 2, 174 field examinations, providing an average accuracy of 98%. Researchers conducted 11 studies involving the reliability of independent analyses of 1,609 sets of charts from field examinations confirmed by independent evidence, providing an average accuracy of 92%.

Some studies that have been conducted in attempts to determine the accuracy of the polygraph examination have been conducted in laboratory settings. During examinations conducted in a laboratory setting, the deceptive examinees normally will lack any significant fear of detection and there is little if any fear of error by the truthful examinee. Although in some laboratory studies money may be rewarded to the examinees that are able to defeat the test, this is hardly comparable to the loss of liberty or life as found in field studies / real life situations.

In a study conducted by Normon Ansley in 1995, he found that the average anticipatory heart rate of the laboratory examinees was 73.7 beats per minute, while the field average was 87.3 beats per minute. In studies of the accuracy of the polygraph examination, the laboratory settings need to be matched as closely as possible to the conditions of actual field cases in attempts to create the same level of arousal in the laboratory as in field studies. If a lie is important to an examinee, the response will differ than if the lie is not important to the examinee, which may be found to be the case in some laboratory settings when the lie may not be made important to the examinee. In real life cases, using test structures that have found to produce valid and reliable results, and by evaluating the results using a consistent set of values to describe the physiological responses of the examinee recorded by the instrument, the results of the examination will be very accurate in determining truthfulness or deception. Test structure techniques which allow for numerical scoring and standard interpretation rules have shown to be highly accurate.

<<Back | Home