The practical value of polygraph testing depends on at least five conceptually different factors that are often not distinguished:
The ability to detect deception from polygraph charts—by analyzing the data collected by polygraph instruments (i.e., psychophysiological detection of deception).
The ability of an examiner to detect deception by using other cues in the polygraph examination (what can be called detection of deception from demeanor).
The deterrent effect of a screening procedure that potential examinees believe can detect their deception or falsely identify them as deceptive.
The ability of the procedure to elicit admissions or confessions because of any of the above factors.
The ability of the procedure to foster public confidence in law enforcement and national security.
The first of these corresponds to the validity of polygraph testing. The others, particularly the last three, relate to what can be termed the utility of polygraph testing.11
It is important to recognize that none of these five elements is unique to polygraph testing. Any interrogation technique that includes physiological measures may combine all of them; traditional investigative techniques that do not use physiological measures often combine all the others. It has been argued, however, that adding a credible physiological measure to an interrogation procedure increases utility not only because of the validity of the physiological test but also by enhancing the other elements. To evaluate polygraph testing for practical purposes, one must therefore consider not only its validity (normally defined in terms of the physiological test), but also its effects on other elements of the interrogation procedure.
What is unique to psychophysiological testing and not common to all interrogation techniques—and what is central to our investigation of its validity—is the capability for the detection of deception that comes from the physiological data collected and the way those data are analyzed. Although the polygraph may enhance the utility of interrogation in ways that are unrelated to its validity, such benefits would be shared equally by any other adjunct to interrogation that was applied similarly and that had