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Research & Studies

Research / Case Studies:

  • Air Force Research Laboratory, Rome, NY, October 2000.  Funded by the National Institute of Justice, a three-year study by the AFRL determined that voice stress analysis achieved an accuracy rate of 100% when used to detect stress in 45 utterances in known-conclusion cases.

  • The Psychological Stress Evaluator (Voice Stress Analysis),  A validation study, Michael P Kratz, Lt Chief Polygraph Examiner, Howard County Police Department, MD. 1987:


There is a 100% inter-examiner reliability with VSA compared to 93% with polygraph.  This study’s finding of 100% corroboration between results and independent corroboration present a successful validation.  The physiological change in the voice, which is detected by the VSA is a valid indication of the stress interpreted to detect attempted deception.  The VSA is a valid component either in tandem with the polygraph or used as a single instrument of stress.Truth and deception is an art.  Results found in the study indicate clearly that the frailty of the system is the human factor.  The instrumentation appears to perform just as it was designed to perform.  Audio Stress Analysis seems to be valid in detecting various psycho-physiological parameters in truth and deception so that a properly trained examiner utilizing standard techniques can evaluate these changes and thus utilize the instrument in truth and deception.  The compliance between evaluators and the known results with 258 evaluation replies is 96,12%.  With examiners added to the group reliability jumped to 96,78%.  It would appear that the validation study asked for in the article, The Psychological Stress Evaluator:  A Recent Development in Lie Technology, and the validation found by Kratz and Dahm, and reported by Stanley and Kriete in their address to the International Society of Stress Analysts in Chicago in 1973 is authenticated by this study.



Polygraph collects data from two pneumo tubes applied around the subject’s upper chest and stomach.  A blood pressure cuff is attached to the subject’s upper left arm.  Set of two fingerplate electrodes measure galvanic skin resistance (fitted to two fingertips of the right hand).  Subject must sit still and not move to ensure the accuracy of data collected.


Subject can manipulate breathing cycles, which will seriously affect the outcome of an examination.  Subject can affect a “sphincter pinch” which also renders the examination worthless.  Subject can (unseen) flex and tighten various major muscles that will again seriously affect the examination results.  Subject can ingest various easily obtained medications that will render the polygraph examination to be worthless – all without the knowledge of the examiner.  The only way to overcome chemically induced countermeasures is to have subjects donate a urine sample under controlled circumstances – and which is not feasible 99% of the time.

VSA (Voice Stress Analysis):

VSA collects data from the voice. One of the psycho-physiological responses to lying (lying induces psychological stress in a subject as lying is contrary to default human behaviour) is an involuntary tightening of muscles surrounding the larynx.  The result is a lowering of the frequency at which the subject’s voice normally oscillates.  This oscillation has been termed the “Lippold Tremor”.  The frequency lowering of the “Lippold Tremor” creates an unmistakable tracing, which the trained examiner will score as Deception Indicated.  There is no way that the subject can manipulate the Lippold Tremor.  “Playing” with the voice will make no difference.  The subject is totally unable to manipulate the Lippold Tremor.  A subject would have ingested a vast amount of pharmaceuticals to affect the Lippold Tremor to the extent that he/she would be visibly intoxicated and therefore unsuitable to be examined/tested.

VSA is reliably accurate to the extent that certain polygraph manufacturers have added a version of VSA to their instrumentation.  That is tacit admission that VSA is a reliable parameter.

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