have been in practice in other areas, but the most “successful” expert systems for medical diagnosis require a substantial body of theory or empirical knowledge that link clearly identified measurable features with the condition being diagnosed (see Appendix F). For screening uses of the polygraph, it seems clear that no such body of knowledge exists. Lacking such knowledge, the serious problems that exist in deriving and adequately validating procedures for computer scoring of polygraph tests (discussed above) also exist for the derivation and validation of expert systems for combining polygraph results with other diagnostic information.

Insufficient scientific information exists to support recommendations on whether or how to combine polygraph and other information in a sequential screening model. A number of psychophysiological techniques appear promising in the long run but have not yet demonstrated their validity. Some indicators based on demeanor and direct investigation appear to have a degree of accuracy, but whether they add information to what the polygraph can provide is unknown (see Chapter 6).


The practical use of polygraph testing is shaped in part by its legal status. Polygraph testing has long been the subject of judicial attention, much more so than most forensic technologies. In contrast, courts have only recently begun to look at the data, or lack thereof, for other forensic technologies, such as fingerprinting, handwriting identification and bite marks, which have long been admitted in court. The attention paid to polygraphs has generally led to a skeptical view of them by the judiciary, a view not generally shared by most executive branch agencies. Judicial skepticism results both from questions about the validity of the technology and doubt about its need in a constitutional process that makes juries or judges the finders of fact. Doubts about polygraph tests also arise from the fact that the test itself contains a substantial interrogation component. Courts recognize the usefulness of interrogation strategies, but hesitate when the results of an interrogation are presented as evidentiary proof. Although polygraphs clearly have utility in some settings, courts have been unwilling to conclude that utility denotes validity. The value of the test for law enforcement and employee screening is an amalgam of utility and validity, and the two are not easily separated.

An early form of the polygraph served as the subject of the wellknown standard used for evaluating scientific evidence—general acceptance—announced in Frye v. United States (1923) and still used in some courts (see below). It has been the subject of a U.S. Supreme Court decision, United States v. Scheffer (1998), and countless state and federal deci-

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