Methodology and Accuracy
The McQuiston-Ford algorithm used for Voice Stress Analysis is reliably accurate. and 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 known-conclusion responses.
(Available from http://anype.com/SURF/http://extraafrl.af.mil/news/fa1100/features/detects:stress:feature.pdf). The recorded "micro tremors" in a person's voice are converted via the algorithm into a scorable voice gram. The discrepancy in researched accuracy may result from incorrectly trained or non-trained persons utilizing the technology incorrectly. This is evident by some Polygraphists trying to "test" VSA technology without having received accredited training in the use thereof.
Polygraph-only associations have disputed the accuracy of VSA although many accredited polygraphists have trained in the use of VSA. The traditional analysis and scoring of voice-grams by means of assigning 'percentages' is time consuming, has been replaced by 7 position scoring and lately by AVSA PRO auto scoring.
In 2002, Clifton Coetzee (Polygraph & VSA Instructor) devised a scoring method for voice grams incorporating the 'UTAH 7 Point' scoring system, as used by modern day polygraphists. Reactive or Responsive patterns are assigned a weighting of +3 to -3.
The use of CQT testing protocols developed by John Reid and Cleve Backster are used for greater reliability of VSA results. It is important that VSA examiners be skilled in the use of enforced, timed pauses between stimulus (question) and response (answer). As in the polygraph situation, the fight or flight response has onset and conclusion delays, which must be considered by examiners to achieve reliable results.
In 2010 through to 2011, Clifton Coetzee and Jean-Louis Gouin (Alpes-Software: Developer of original Diogenes Lantern, which is now re-labelled as TDT )developed AVSA PRO, which is a unique, evolutionary, fully automatic VSA system. AVSA PRO is programmed to cater for cadence control being consistent in every question posed. Examiner induced errors have been eliminated. AVSA PRO is based on a neural network - another major innovation in the worldwide vsa industry. Scoring of automatically captured and numerically identified voice wavs is according to the neural network database, developed from Expert blind scoring of 000's of voice wavs, with the input of known outcomes. and
The American Polygraph Association's website lists conclusions from multiple studies, into the accuracy of voice stress analysis as a means of detecting the subject's truthfulness. Some researchers or polygraph professionals cast doubt on the validity of the results of such tests; many describe the results as no better than chance.
The National Academy of Sciences (USA) severely criticized the validity of APA studies into polygraph as "biased, unscientific and industry funded." The NAS study concluded that there has been no scientific advancement in polygraphy. Further, that polygraphy was unreliable as a lie detection technology. ( http://anype.com/SURF/http://www.nap.edu/openbook.php?isbn=0309084369 )
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