What the American Polygraph Association Says

From the website of the American Polygraph Association:

A steady pace of improvements in techniques and technologies has allowed the polygraph to remain the gold standard among the methods available for verification of truthfulness. While other technologies come and go, the longevity of the polygraph is a testament to its power to uncover those who would deceive.

Hmm... Was the longevity of the practice of bleeding medical patients a testament to its power to heal? Perhaps the longevity of some practices is unrelated to their effectiveness. Longevity isn't a very strong argument to start with.

Professor Stephen E. Fienberg, Chairman, Committee to Review the Scientific Evidence on the Polygraph, National Academy of Sciences, has this to say about the polygraph:

Polygraph testing has been the gold standard, but it's obviously fool's gold.

The American Polygraph Association website says that the problem of accuracy is one of differing methods of measuring it. Critics, they say, "who often don't understand polygraph testing, classify inconclusive test results as errors." This isn't an error, they say, but I imagine that if you are accused of murder, and you are innocent, you might want a more accurate result from a polygraph test than "inconclusive."

They explain the problem: "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.)" They may have a reasonable argument there in some ways.

On the other hand, what is more interesting, is that even in an argument from the biggest promoters of the polygraph, they use an example of 87.5% accuracy. That might sound good until you realize that of a 100 people tested in a murder case, about 10 innocent people would be found to be "lying." And there would also be 20 "inconclusive" results, which might include both innocent people and murderers.

Looked at another way, of a 100 murderers, 10 would be found to be telling the truth, and 20 would have inconclusive results. Out of 100 murders, 30 would not be identified, according to the accuracy assumed in the example.

But let's look at their method again, with a new example. Suppose 100 innocent people were questioned about a crime, and one was found to be telling the truth, while the other 99 tests were "inconclusive." This would appear to be a relatively useless test, right? It correctly identifies just 1 out of 100 innocent people, leaving a cloud of suspicion over the other 99. Yet, measuring the results the way the American Polygraph Association does, the accuracy would be 100%.

Another quote from the APA web site:

To date, there has been only a limited number of research projects on the accuracy of polygraph testing in the pre-employment context, primarily because of the difficulty in establishing ground truth. However, since the same physiological measures are recorded and the same basic psychological principles may apply in both the specific issue and pre-employment examinations, there in no reason to believe that there is a substantial decrease in the accuracy rate for the pre-employment circumstance.

In other words, while strongly promoting the use of polygraph testing for employment screening, they admit that there is no evidence for its accuracy. They just assume that it will work as well in this very different context.

Somewhere on the American Polygraph Association website, you can find a few mentions of scientific evidence. Here is one small excerpt: "Researchers conducted 41 studies involving the accuracy of 1,787 laboratory simulations of polygraph examinations, producing an average accuracy of 80%. Researchers conducted 16 studies involving the reliability of independent analyses of 810 sets of charts from laboratory simulations producing an average accuracy of 81%."

Is a test that would identify 200 out of a thousand innocent job applicants as liars really something that should be promoted? Maybe this helps explain item number 7 from the American Polygraph Association's Checklist for the Polygraph Examiner: "Carry a minimum of $50,000 or equivalent professional liability coverage."

Continues here... Polygraph Accuracy: More Interesting Facts

Beat a Lie Detector Test | What the American Polygraph Association Says