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The Polygraph and Lie Detection
incomplete model for actual polygraph screening, the resulting data seem reasonably relevant. An important screening-related question that can be addressed by such studies is whether polygraph-based judgments that an examinee was deceptive on the test are attributable to polygraph readings indicating deception on questions that the examinee actually answered deceptively or to false positive readings on other questions that were answered truthfully. While simply identifying that an examinee was deceptive may be sufficient for many practical purposes, scientific validity requires that polygraph charts show deception only when deception was actually attempted.
Barland, Honts, and Barger (1989) report the results of three experiments. In their first study, the questions and examination methods differed across examiners, and the false negative rate was extremely high (66 percent of the guilty examinees are not identified as deceptive). There was also wide variation in the formats and the standards used to review examinations. In their second study, the authors compared multiple-issue examinations with multiple single-issue examinations. While this study achieved higher overall sensitivity, there was little success in determining which guilty examinees committed which among a number of crimes or offenses. Their third study retested a number of subjects from the first study, and its results are hence confounded. Collectively, results of these three studies do not provide convincing evidence that the polygraph is highly accurate for screening.
Three U.S. Department of Defense Polygraph Institute (DoDPI) studies designed to validate and extend the Test of Espionage and Sabotage (TES) (U.S. Department of Defense Polygraph Institute, 1995a, 1995b; Reed, no date) showed overall results above chance levels of detection but far from perfect accuracy. One of these studies passed our screening (Reed, no date), and it reported data indicating an accuracy (A) of 0.90, corresponding to a sensitivity of approximately 85 percent and a specificity of approximately 78 percent. All three studies share biases that make their results less convincing than those statistics indicate. Deceptive examinees were instructed to confess immediately after being confronted, but nondeceptive examinees whose polygraph tests indicated deception were questioned further, in part to determine whether the examiner could find explanations other than deception for their elevated physiological responses. Such explanations led to removal of some subjects from the studies. Thus, an examiner classifying an examinee as deceptive received immediate feedback on the accuracy of his or her decision, and then had opportunity and incentive, if the result was a false positive error, to find an explanation that would justify removing the examinee from the study. No comparable search was conducted among true positives. This process biases downwards the false positive rate observed in association with any