Joe Bauman of the Deseret News reports in this single-source article on polygraphy:
The accuracy of polygraph tests compares well with that of other forensic techniques — but sometimes emotions can short-circuit the results, a national expert says.
The tests record physiological responses to questions. The queries usually cover both a crime under investigation and matters that are irrelevant or simply technical such as: Is today Friday? Responses to these comparison questions are checked against responses to relevant questions.
But if a subject is overwrought, the responses may not be significantly different between the two types of questions.
Take a case where a homicide occurred and the victim’s spouse is to be questioned, said Frank Horvath, professor in the School of Criminal Justice, Michigan State University, East Lansing. A past president of the American Polygraph Association and an avowed proponent of the validity of the tests, he was interviewed by telephone on Friday.
In that theoretical case, if an examiner were to “test the living spouse the day after the crime occurred, there would be an awful lot of emotion intermixed with this and that would not produce a useful outcome.”
The result could be inconclusive, he noted. “Sometimes there’s just no way around it.”
Horvath said a way to resolve that might be to test later, when emotions have settled down.
Polygraphs are not lie-detectors, he emphasized. The machine records physiological reactions to questions, and trained examiners usually can tell if the subject’s responses are truthful.
The machine records reactions to three conditions, all of which can change under stress, including the stress of lying: breathing; blood pressure and pulse; and skin electrical conductivity.
During a pretest interview, the examiner carefully discusses the case and goes over every question. The subject must know what the questions are, word for word, so he is not surprised by anything. He must not give a startled, and therefore misleading, response.
Usually the test consists of 10 or 11 questions that can be answered by yes or no. Of these, three or four are relevant to the investigation and the rest are irrelevant or comparison questions.
During testing, when the subject is connected to the monitors, “that list of questions is repeated,” usually three or four times. Pauses of 20 or 30 seconds separate the questions, allowing the physical response to occur and subside.
“We look for consistency of responses to the same questions,” Horvath said.
Usually when a person is telling the truth about a crime he will “produce more dramatic and consistent responses to the comparison questions,” he said.
“If they’re not telling the truth, the opposite occurs.”
But if the responses to both types of questions are about the same, “that’s an inconsistent outcome.” The data might not be strong enough for an examiner to reach a conclusion about truthfulness .
“Sometimes there could be confusion, sometimes the person is emotionally distraught,” he said. “We don’t know everything that produces inconclusive” results.
Usually that happens when a subject is not properly prepared for the testing, he believes.
Child abductions are common throughout America, he said, and so is the use of polygraph testing in those cases.
“In this kind of case, polygraph testing plays an extremely critical role.”
The tests are used daily with great success. The public should not consider a polygraph test to be a last-ditch investigation when all else has failed.
How accurate are the tests?
“This is an issue that has not been resolved, and we have very strongly polarized views,” Horvath said. Nobody says they are perfect, and nobody says they don’t work.
Professor Frank Horvath is dead wrong when he claims “nobody says [polygraph tests] don’t work.” Since September 2000, AntiPolygraph.org has been working to alert the public to the fact that polygraph “testing” is a pseudoscientific fraud that only “works” to the extent that it succeeds in eliciting admissions/confessions from the naive and the gullible. Among the gullible is reporter Joe Bauman, whom Frank Horvath evidently misled into believing that irrelevant questions such as, “Is today Friday?” are used as comparison (or “control”) questions, when such is not the case, as readers of The Lie Behind the Lie Detector are well aware.