Question 1

How accurate is a polygraph test?

Accepted Answer

According to a 2003 National Research Council study reviewed in this article, polygraph tests can distinguish lying from truth-telling at rates above chance but well below perfection. Accuracy varies widely across studies and is difficult to measure precisely. Real world accuracy is almost certainly lower than laboratory results suggest, because field conditions involve far more variation in examiners, examinees, and circumstances than controlled studies can replicate.

Question 2

How does a polygraph test work?

Accepted Answer

A polygraph measures physiological responses including blood pressure, respiration rate, and skin conductance (perspiration) while a subject answers questions. The assumption is that deception produces detectable physiological changes. However, many factors unrelated to lying, such as anxiety about being tested, also produce those same responses. This makes the polygraph intrinsically susceptible to false positives (identifying truthful people as deceptive) and false negatives (missing actual liars).

Question 3

Are polygraph results admissible in court?

Accepted Answer

Admissibility varies by jurisdiction. Most federal courts and many state courts exclude polygraph evidence, citing high error rates and the risk that juries will give it undue weight. Some jurisdictions allow it when both parties stipulate in advance. The Supreme Court upheld a military rule excluding polygraph evidence in United States v. Scheffer (1998), noting that the scientific community remains deeply divided on its reliability.

Question 4

Can you beat a polygraph test?

Accepted Answer

Research suggests that people trained in countermeasures, such as controlled breathing or deliberate muscle tension during control questions, can significantly reduce a polygraph's ability to detect deception. The 2003 National Research Council study found that countermeasures pose a serious threat to polygraph accuracy, particularly in security screening contexts where the consequences of passing are high and examinees have strong motivation to prepare.

Question 5

Should polygraphs be used for national security screening?

Accepted Answer

The authors argue against heavy reliance on polygraphs for security screening. Because screening involves generic questions rather than specific incidents, ambiguity about what constitutes a truthful answer further reduces accuracy. In a population where actual spies or security threats are rare, even a test with modest error rates will produce far more false positives than true detections, potentially wasting investigative resources and wrongly implicating innocent people.

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