How accurate is a polygraph?

While the polygraph technique is highly accurate, it is not infallible and errors can occur. According to the American Polygraph Association over 250 studies have been conducted on the accuracy of polygraph testing during the past 25 years. Recent research reveals that the accuracy of the new computerized polygraph stytem is close to 100%.

Most errors occur with inexperienced polygraph examiners. Just as one doctor can look at an x-ray, and not see a problem, while the next, more experienced doctor can, so it goes with polygraph charts.

Occationaly you will hear reports from those who fear the polygraph may not be accurate. The APA answers them with this:

One of the problems in discussing accuracy figures and the differences between the statistics quoted by proponents and opponents of the polygraph technique is the way that the figures are calculated. At the risk of over simplification, critics, who often don't understand polygraph testing, classify inconclusive test results as errors. In the real life setting an inconclusive result simply means that the examiner is unable to render a definite diagnosis. In such cases a second examination is usually conducted at a later date. To illustrate how the inclusion of inconclusive test results can distort accuracy figures, consider the following example: If 10 polygraph examinations are administered and the examiner is correct in 7 decisions, wrong in 1 and has 2 inconclusive test results, we calculate the accuracy rate as 87.5% (8 definitive results, 7 of which were correct.) Critics of the polygraph technique would calculate the accuracy rate in this example as 70%, (10 examinations with 7 correct decisions.) Since those who use polygraph testing do not consider inconclusive test results as negative, and do not hold them against the examinee, to consider them as errors is clearly misleading and certainly skews the figures.