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19 Thought Provoking Polygraph Accuracy Statistics

Polygraph examinations, which are routinely referred to as lie detectors, are often considered one of the best ways to tell if someone is actually saying something that is true. They have become an icon of popular culture and most people know that a spiked reading means a lie has been told. Even television shows are creating dramatic episodes where loved ones take lie detector tests to determine if they are being truthful about specific events.

Most psychologists, however, are in agreement that there is little evidence that a polygraph test can actually detect a lie.

So why even bother with a lie detector test? After all, their results aren’t admissible in court. The truth about a polygraph is this: it measures nervous excitement more than anything. The thought process is that if someone is telling the truth, then they will remain calm and not have this nervous energy. That means the very heart of the issue of polygraph accuracy is based on assumptions that are being made by operators – assumptions that are sometimes generated based on information that might not be true regarding a test participant.

Three Fast Facts About Polygraph Accuracy

1. The American Polygraph Association claims that polygraphs are accurate over 90% of the time when properly administered and bias has been removed from the equation.
2. Critics of the polygraph system say that the evidence shows these lie detectors are only accurate about 65% of the time – hardly better than random chance.
3. The issue with polygraphs is that they can do a reasonably good job of finding lies, but offers a 50/50 chance of showing the operator that an honest person actually told a lie.

Takeaway: The one real issue of polygraph accuracy is that the entire test is subjective. Not only does the operator of the polygraph need to judge what your baseline results are for accuracy, but they must also judge when they believe there is a spike in your nervous energy. How is this problematic? Because there is no way to show what your normal baseline should be! There can be variances every day and only an average of readings over a period of time can truly establish a baseline. This also means that faking through a polygraph can easily be done just by skewing the results of the baseline so that there is more nervous energy with honest answers.

What Are Some Things to Consider About Polygraphs?

1. When computers take over as the primary controller of the polygraph, the accuracy of the test climbs toward 100%.
2. In 2001, Attorney General John Ashcroft estimated that the false positive rate for the typical polygraph examination was 15%.
3. In 1998, the Supreme Court of the US allowed states to ban the results of polygraphs because their results could not be verified.
4. In a 1996 study of criminal cases where a lie detector was used, the control question tests were found to be up to 96% accurate.
5. A 1997 survey of over 400 psychologists estimates that the test’s average validity rates for success were 61%.
6. Psychologists at the University of Utah published a report in 1994 that suggest if polygraph participants performed a series of behaviors, including biting their tongue and counting backwards by 7s during the control questions, the results of every polygraph could be skewed.
7. Research shows that if 10,000 people took a polygraph, about 1,600 people on average would end up failing the test.
8.“Proponents will say the test is about 90% accurate. Critics will say it’s about 70% accurate.
9. A polygraph test consists of only “yes” or “no” questions.

Takeaway: As a crime measurement tool, there are some pros and some cons with a polygraph test. The good is that people are so scared of a lie detector sometimes that they’ll just offer up some information voluntarily because they’re afraid of what the results would say. Rather than be accused of lying, they simply tell the truth and let the cards fall where they may. The bad is that it can be nearly impossible to find people who don’t want to be found and because a major component of this exam is to measure the guilt someone is feeling, false positives are definitely something that could become quickly problematic. Overall, it’s very easy to see why so many studies give lie detector tests a failing grade when it comes to accuracy.

Are Polygraph Tests Completely Worthless?

1. According to the National Academy of Sciences [NAS], when you eliminate people who are trained in countermeasures from the results of a polygraph, the overall accuracy is about 85%.
2. When including analysis of 7 field studies that involve specific incidents when polygraphs were used, a median accuracy of 89% is achieved.
3. Despite the high percentages, however, the NAS determined that polygraph tests have too high a margin of error to provide any useful information.
4. If MRI technology is included in polygraph administration, the base accuracy rates jump from 61% to 76%.
5. Because there is a wide spectrum of polygraph tests, there is no actual standard measurement of success or failure that can be applied to test results.
6. The Utah technique of polygraph test results have an overall accuracy rate of 93.9%.
7. 19 states allow polygraphs to be admissible in the guilt phase of a trial only after stipulation between the defendant and prosecutors.

Takeaway: One of the primary reasons why lie detectors are thought to be inaccurate is because of the case of Aldridge Ames. In one instance, he fed plausible information to the administrator of a polygraph and this was determined to be truthful enough. On the second polygraph, he was cleared of guilty activity, but only initially. Ames might proclaim he could be a lie detector, but what he could really beat were the protocols for lie detection. That, at the core, is the issue with polygraph accuracy. Different administrators have different protocols, even if just slight variances, and that in itself can skew the results.

How a Polygraph Test Works

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