Why Not Voice Stress?

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Many people confuse voice stress analysis with polygraph examinations, mainly due to the fact that a large number of individuals offering voice stress analysis services mislead their client base by introducing themselves as polygraph examiners. This last statement in itself should answer the question of: "Why Not Voice Stress Analysis?"

To be absolutely clear: A Computerised (or other) Voice Stress Analysis (VSA) operator is NOT a polygraph examiner. Compare it if you will to an acupuncturist representing himself as a medical doctor.

The major differences between Forensic Psycho-Physiological Detection of Deception Examinations (Polygraph) and Voice Stress Analysis are:

  • A polygraph instrument collects forensic data from at least three different systems in the human body ex. Respiratory Activity, Sweat Gland Activity and Cardiovascular Activity. Voice stress analysis records "microtremors" in the voice box.
  • Polygraph Testimony is accepted as evidence at the South African CCMA. Voice Stress Analysis is not being accepted as evidence by the CCMA.
  • Accuracy of voice stress analysis is far lower than a polygraph.


For several years companies, organisations and governments have been the target of determined marketing efforts by the operators and manufacturers of voice-based lie detectors. The principal sales strategy since the early 1970s has been that their particular voice device is more accurate and cost less than the polygraph. These sales strategies unfortunately appeal to cash-strapped companies, organisations and governments - and if true, the devices would quickly come to replace the current gold standard, the polygraph. There are at least 10 different voice devices sold in the US, freeware packages are on the Internet, and a burgeoning list of smartphone applications. Why, then, have voice devices not come to surpass the polygraph in international law enforcement and government over the past 40 years?

It is a fact that voice lie detectors trail far behind the polygraph, even in sheer number of units. And though some voice device manufacturers claim to have sold X number of their devices to various organizations, a significant number of international entities discarded them quickly after discovering that the reality of the systems fall far short of what manufacturers had promised.

Voice device manufacturers would blame their limited market impact on the bias of polygraph examiners, but the truth goes deeper. The first reason for the failure of voice lie detectors to capture the field is simple: they are highly unreliable. More than that, they have been discredited by a large and expanding body of independent scientific research. This is the main reason they are banned by eg, the US Department of Defence. With such dismal accuracy they are little more than very expensive interrogation props.

Overall, this research and the few controlled tests conducted over the past decade offer little or no scientific basis for the use of the computer voice stress analyzer or similar voice measurement instruments as an alternative to the polygraph for the detection of deception. The practical performance of voice stress analysis for detecting deception has not been impressive. (US Academy of Sciences - 2003)