Rep. Gary Condit believes the independent polygraph exam he passed proves he was not involved in the disappearance of missing intern Chandra Levy. But while often accurate, polygraphs are not foolproof, experts say.
"Proponents will say the test is about 90 percent accurate. Critics will say it's about 70 percent accurate," said Frank Horvath of the American Polygraph Association. "Many people refer to polygraph tests as lie detector tests, and that's a bit of a misnomer.
"There is no test that can detect lies. … The process in which the questions are asked and the sequence of the questions may affect how a person reacts," Horvath said. "Since the process is not perfect, that could lead to the possibility of error, and that's why there's problems when trying to get them in the courts."
Polygraph literally means "many writings" and it refers to ways in which several physiological activities are simultaneously recorded during a test. During a standard polygraph test, examiners monitor at least three bodily reactions to determine whether a person is truthfully answering questions: respiratory rate, sweat gland activity, and cardiovascular activity.
Condit Test Done Independently
Condit's attorney, Abbe Lowell, announced that the California congressman had passed an independent exam given by Barry Colvert, a former 35-year veteran FBI polygraph examiner, and not investigators involved in the case. Lowell said the test showed "no deception" by Condit.
But Washington, D.C., police called the test Condit took "self-serving" because authorities did not take part and had not seen the full results. "We'll take that information like we take everything, and examine it," said Assistant Chief of Police Terrance Gainer.
Levy has been missing since May 1, and her parents had called on Condit to take a polygraph. The congressman has admitted to police that he had an affair with the young woman, according to sources.
But Levy attorney Billy Martin said the missing intern's parents were "very disappointed" about the privately administered polygraph. "We're wanting him to be fully cooperative and not cooperate on his terms," Martin told reporters.
Polygraph Takers Not Ambushed
Whether given privately or by authorities, a polygraph subject should not be ambushed with surprise questions. As part of the pre-test phase, the polygraph examiner helps familiarize the examinee with the testing procedures and discusses the questions that will be asked.
Rubber tubes are placed over a subject's chest and abdominal area to measure respiratory activity; small metal plates attached to the fingers record sweat gland activity, and a blood pressure cuff or similar instrument will monitor the cardiovascular system. Voice stress is not measured.
A polygraph test consists of only "yes" or "no" questions. According to Nate Gordon, founder of Philadelphia-based Academy for Scientific Investigative Training, the test has three phases: a pre-test, a chart-collection phase and then test data analysis. During pre-test, Gordon says, the examinee undergoes tests to make sure he or she is mentally and physically capable of undergoing a polygraph exam.
"During this time, examiners may have a person lie and examine the person's body movements to see if they can tell if they're lying," Gordon said.