Polygraph Testing

Overview of the Polygraph

A polygraph machine records the body's involuntary responses to an examiner's questions in order to ascertain deceptive behavior. The test measures physiological data from three or more systems of the human body—generally the respiratory, cardiovascular, and sweat gland systems—but not the voice. There are other tests that test the voice for deception.

Polygraph Testing usually takes around 2 hours from beginning to end and consists of three different phases; pre-test interview, collection of charts, and analysis of charts.

When a person takes a polygraph test, four to six sensors are attached to the person. A polygraph is a machine in which the signals from the sensors are recorded on a single strip of moving paper. The sensors usually record:

● The person's breathing rate

● The person's pulse

● The person's blood pressure

● The person's perspiration

Sometimes a polygraph will also record things like arm and leg movement.

When the polygraph test starts, the questioner asks three or four simple questions to establish the norms for the person's signals. Then the real questions being tested by the polygraph are asked. Throughout questioning, all of the person's signals are recorded on the moving paper. Both during and after the test, a polygraph examiner can look at the graphs and can see whether the vital signs changed significantly on any of the questions. In general, a significant change (such as a faster heart rate, higher blood pressure, increased.

History of the Polygraph

"Polygraph" means literally "many writings," referring to the method of recording several physiological activities at the same time. William M. Marston invented the first lie detector in 1917. Marston claimed he could reveal verbal deception by observing levels of systolic blood pressure. However, in 1923, the D.C. Court of Appeals stated that there was not enough scientific evidence to support Matston's lie detector machine. Roughly a century later, Leonarde Keeler invented a machine and school for examiners that paved the way for the modern use of polygraph testing, especially in the legal realm. The majority of uses of polygraph testing appear to be on behalf of private employers, the next greatest number are in the context of local criminal justice investigations, and the remainder are done by the Federal Government

Types of Polygraph Testing

The most widely used test format for subjects in criminal incident investigations is the Control Question Test (CQT). The CQT compares responses to "relevant" questions (e.g., "Did you shoot your wife?"), with those of "control" questions. The control questions are designed to control for the effect of the generally threatening nature of relevant questions. Control questions concern misdeeds that are similar to those being investigated, but refer to the subject's past and are usually broad in scope; for example, "Have you ever betrayed anyone who trusted you?"

An alternative polygraph procedure is called the Guilty Knowledge Test (GKT). A GKT involves developing a multiple-choice test with items concerning knowledge that only a guilty subject could have. A test of a theft suspect might, for example, involve questions such as "Was $500, $1,000, or $5,000 stolen?" If only a guilty suspect knows the correct answer, a larger physiological reaction to a correct choice would indicate deception. With a sufficient number of items, a psychometrically sound evaluation could be developed. GKTs are not widely employed, but there is great interest in doing so. One limitation of the GKT is that it can be used only when investigators have information that only a guilty subject would know. The interpretation of "no deception" is also a potential limitation, since it may indicate lack of knowledge rather than innocence.

Validity of Polygraph Testing

The accuracy (i.e., validity) of polygraph testing has long been controversial. An underlying problem is theoretical: There is no evidence that any pattern of physiological reactions is unique to deception. An honest person may be nervous when answering truthfully and a dishonest person may be non-anxious. Also, there are few good studies that validate the ability of polygraph procedures to detect deception. As Dr. Saxe and Israeli psychologist Gershon Ben-Shahar (1999) note, "it may, in fact, be impossible to conduct a proper validity study." In real-world situations, it's very difficult to know what the truth is.

A particular problem is that polygraph research has not separated placebo-like effects (the subject's belief in the efficacy of the procedure) from the actual relationship between deception and their physiological responses. One reason that polygraph tests may appear to be accurate is that subjects who believe that the test works and that they can be detected may confess or will be very anxious when questioned. If this view is correct, the lie detector might be better called a fear detector.

Some confusion about polygraph test accuracy arises because they are used for different purposes, and for each context somewhat different theory and research is applicable. Thus, for example, virtually no research assesses the type of test and procedure used to screen individuals for jobs and security clearances. Most research has focused on specific incident testing. The cumulative research evidence suggests that CQTs detect deception better than chance, but with significant error rates, both of misclassifying innocent subjects (false positives) and failing to detect guilty individuals (false negatives).

Research on the processes involved in CQT polygraph examinations suggests that several examiner, examinee, and situational factors influence test validity, as may the technique used to score polygraph charts. There is little research on the effects of subjects' differences in such factors as education, intelligence, or level of autonomic arousal.

Evidence indicates that strategies used to "beat" polygraph examinations, so-called countermeasures, may be effective. Countermeasures include simple physical movements, psychological interventions (e.g., manipulating subjects' beliefs about the test), and the use of pharmacological agents that alter arousal patterns. Despite the lack of good research validating polygraph tests, efforts are on-going to develop and assess new approaches.

Admissibility in Court

It seems to be the public's general opinion that the results of polygraph testing is not allowed in court under any circumstances.

The truth is that Polygraph results are admissible in most courts across the country. The Supreme Court has yet to rule on the issue of admissibility so it has been up to individual jurisdictions to allow or disallow them. There are some jurisdictions that have absolute bans on admitting polygraph results, but most allow them.

Cases

United States v. Scheffer, 523 U.S. 303 (1998).

The United States Supreme Court examined the admissibility of polygraph results in court, stating:

The contentions of respondent and the dissent not withstanding, there is simply no consensus that polygraph evidence is reliable. To this day, the scientific community remains extremely polarized about the reliability of polygraph techniques. Some studies have concluded that polygraph tests overall are accurate and reliable. See, e.g., S. Abrams, The Complete Polygraph Handbook 190-191 (1968) (reporting the overall accuracy rate from laboratory studies involving the common "control question technique" polygraph to be "in the range of 87 percent"). Others have found that polygraph tests assess truthfulness significantly less accurately – that scientific field studies suggest the accuracy rate of the "control question technique" polygraph is "little better than could be obtained by the toss of a coin," that is, 50 percent.