Execution Fuels Debate About Lie Detector Tests


Even if he was innocent, few experts think that Roger Keith Coleman, the convicted rapist and murderer from Virginia, could have passed a polygraph examination on his execution day.

Strapped in and wired up to a machine that bore more than a passing resemblance to the device that would electrocute him 12 hours later, Coleman failed the so-called lie detector examination.

It was the 33-year-old man’s last chance to prove his innocence, but almost certainly not his best.

“I would certainly place less reliance on any test done under those circumstances. To me, it was an extremely objectionable thing to do,” said Frank Horvath, president of the American Polygraphy Assn. and a professor of criminal justice at Michigan State University.


“A truthful person has to be calm and collected. But this was Coleman’s last straw. This situation was different from any other,” said Earl F. Kane, a polygrapher with 40 years of experience who advised the convict’s attorneys and tried, unsuccessfully, to monitor the secret examination.

Virginia Gov. L. Douglas Wilder’s apparently unprecedented decision to use polygraph testing as the condemned man’s court of last resort has given a macabre new twist to the longstanding debate over the procedure’s validity and reliability.

Though there are no firm estimates, polygraph experts believe at least 250,000 tests are performed each year in the United States. Before a 1988 federal law banned their use by most employers, about 2 million examinations were done annually, mostly to screen job applicants.

Today, the test is used primarily by police departments, prosecutors and defense attorneys, the Defense Department and various agencies involved in national security. With few exceptions, however, polygraph evidence is inadmissible in federal courts. In about half the states, it is admissible upon agreement of the prosecution and the defense.

Developed in a simpler form in 1917 and in its present form in 1947, the polygraph test purports to work by detecting the physiological changes that accompany the anxiety of telling a lie.

Virtually all polygraph examinations given today are “control question tests.” They work this way:

The examiner formulates about 10 questions that fall into three different categories. Some are termed “irrelevant,” and ask about such trivial subjects as the day of the week. Others are “relevant,” and pointedly query the subject about participation in the crime under investigation: “Were you in the liquor store the night of the robbery?” or “Did you stab Fred?”

The third type, and in many ways most important, is the “control” question. Unlike the relevant questions, these ask about illegal or embarrassing behavior in an intentionally vague way: “Have you ever taken anything that didn’t belong to you?” or “Have you ever intentionally hurt someone?”


The entire battery of questions is discussed with the subject before the test because, by convention, the subject is expected to answer “no” to all relevant and control ones.

For the relevant questions, this is easy--neither the guilty nor the innocent are going to answer “yes” to questions about the crime. The control questions, however, are difficult for any person to answer with a categorial denial. So much of the pretest discussion consists of the subject bearing his breast about past transgressions, which the examiner then “exempts” so that the subject can theoretically answer “no” with a clear conscience once the test begins.

When that time comes, polygraph theory assumes, a guilty person shows high anxiety in response to the relevant questions, but little to the controls. An innocent person, on the other hand, calmly denies a role in the crime, but still cannot muster an unqualified denial to the general questions about wrongdoing. Consequently, he anxiously answers “no” to the control questions--though not as anxiously as if he were baldfacedly denying a serious crime.

These varying levels of anxiety are detected in three ways.


Electrodes on the hand measure the skin’s ability to conduct a weak electric current, which in turn is a function of sweating. Two straps around the chest measure the depth of respiration. A partially inflated cuff on the arm measures blood pressure and pulse. According to polygraphic theory, when most people lie, the skin conductance increases, breaths become shallow and blood pressure rises.

The variables are not equally significant, and part of the examiner’s job is to weigh the totality of physiological “evidence” before reaching a conclusion. A computer program some polygraphers use gives skin conductance 70% of the final score, respiration 20% and blood pressure 10%. (Changes in pulse rate, it turns out, are not felt to be illuminating.)

But polygraphy’s critics say the procedure’s credibility founders long before the weighting of the variables.

“There is no unique physiological reaction to deception,” says Leonard Saxe, a psychologist at the City University of New York, who has written extensively on lie detection. “Someone who is an out-and-out liar can be either extremely nervous or extremely calm. Conversely, somebody who is telling the absolute truth could either be very, very nervous because of the importance of the consequences, or they could be calm.”


Horvath of the American Polygraphy Assn. counters that lying usually causes arousal and that, in any case, polygraph testing relies on the variations in an individual’s physiological responses, rather than the detection of responses that are universal.

“Each person is his or her own standard. What an examiner looks for is patterns of responses,” he said.