An evaluation of polygraphers' judgments: A review from a decision theoretic perspective

A critical discussion of the theory, practice, and evaluation process of the Control Questions Technique (CQT) is undertaken. Sources of possible contamination in the use of this technique are described. Data from seven field studies are reviewed and used to estimate the discriminability of the CQT in real-life situ-ations. A signal detection model is applied to a reanalysis of these seven studies. An attempt is made to derive the value system of the polygraphers who partic-ipated in the seven studies. It is demonstrated that under an assumption of rationality, the examiners tend to value the detection of guilty suspects highly, even in the presence of a high risk of falsely classifying innocent suspects as deceptive. An index of usefulness of the CQT-based evaluation system is denned, and the CQT's range of usefulness is examined as a function of operating costs, possible payoff ratios, and prior probabilities of guilt. The results of these analyses indicate that it is unlikely that the CQT method of lie detection would be useful for determining guilt in a court of law, or even for preemployment screening, though it might be useful for police investigative procedures. Recently we have been witnessing a debat