responses. Other studies, for example by Motley (1974), Horvath (1978, 1979), Lynch and Henry (1979) and Brenner, Branscomb, and Schwartz (1979), have attempted, with limited success at best, to extract information from recorded voice signals to measure stress in analogue studies and then to use the resulting determination as an indirect indicator of deception in much the same way as is done in polygraph research.

Various instruments have been developed over the past 20 years or more that purport to detect deception by means of signals of “voice stress” as reflected in intensity, frequency, pitch, harmonics, and even microtremors. One of the more widely used devices is the computer voice stress analyzer, manufactured by the National Institute for Truth Verification (NITV), which is now used by a number of law enforcement agencies. The underlying theory for the analyzer and some of its predecessor instruments is that the instrument detects physiological microtremors in muscles in the voice mechanism that are associated with deception.

In addition to manufacturing the computer voice stress analyzer, NITV publishes its own journal reporting on the ease of use of the analyzer and its utility in obtaining confessions. NITV also trains and certifies voice stress analysts using protocols for question format and sequences of relevant and irrelevant questions that are remarkably like those used for polygraph testing. The polygraph seems to be the reference point and the target of marketing for NITV and the analyzer. For example, Tippett (1995), writing in the NITV journal, argues that earlier failures to obtain high accuracy rates with the analyzer and similar devices were largely due to the low levels of jeopardy involved in the analog studies. He reports on a study of 54 subjects undergoing mandatory therapy as a condition of probation for past sex offenses and claims to have found “100 percent agreement between the [computer voice stress analyzer] and the polygraph” in the judgments of examiners for the respective techniques. The article does not report on the methods used for scoring or for determining truth, so is not usable for judging the accuracy of the analyzer.

Although proponents of voice stress analysis claim high levels of accuracy, empirical research on the validity of the technique has been far from encouraging. First, the reliability of this method is highly suspect (Horvath, 1978; Waln and Downey, 1987). The agreement between readings of the same voice stress charts by independent analysts is generally low, and correlations of test results between interviews in their original form and recordings of the same interviews transmitted over the telephone are also low (Waln and Downey, 1987). Second, the validity of judgments made on the basis of voice stress analysis appears to be questionable (Lykken, 1981). For example, Horvath (1979) showed approximately chance level of success in identifying deception in mock crime