The accuracy of Voice Stress Analysis

In recent times Computer Voice Stress Analysis (CVSA) has been promoted and used as an alternative to polygraph testing. The manufacturers of CVSA including Truster claim that Voice Stress Analysis can differentiate between truth and deception. Independent research however (see below) disputes that Voice Stress Analysis is an accurate discriminator between truth and deception.

In studies conducted by the US. Department of Defence research concluded that “… very few studies have found that voice stress analysis worked better than chance at detecting deception” and “The preponderance of evidence indicates the polygraph is far more accurate at detecting deception than is voice stress analysis”.

Australian Polygraph Services has been approached by the manufacturers of Computer Voice Stress Analysis on several occasions. Until independent and validated research supports the manufacturers claims Australian Polygraph Services will not use, endorse or support Computer Voice Stress Analysis as a tool for truth verification.

US. Department of Defence Position Statement on Voice Stress Analysis
September 11, 1996

The Department of Defence Polygraph Institute has investigated the scientific value of voice stress analysis. We reviewed the research literature on voice stress analysis. Only one voice stress device, the CVSA, is being widely marketed. We purchased the CVSA, and sent two researchers to the CVSA school for training by the manufacturer. We conducted several studies on voice stress analysis, using standard laboratory voice equipment and software and also using the CVSA device. We solicited the manufacturer’s advice in designing the CVSA studies, and used both our own scientists and CVSA practitioners recommended by the CVSA manufacturer to gather the research data.

Conclusions

To date, we have found no credible evidence in information furnished by the manufacturers, the scientific literature, or in our own research, that voice stress analysis is an effective investigative tool for determining deception.
Few studies have found that voice stress analysis worked better than chance at detecting deception. Unfortunately, these results are not consistent, nor are the reported accuracies nearly as good as those normally reported for the polygraph. Hundreds of studies have shown that when properly trained examiners use the polygraph under controlled conditions, their decisions can be highly accurate in discriminating between truthful and deceptive people.
The preponderance of evidence indicates the polygraph is far more accurate at detecting deception than is voice stress analysis. No Department of Defence agency uses any form of voice stress analysis for investigative purposes.

American Association of Police Polygraphists Position Statement on the Use of Voice Stress Analysis
In order to properly serve the Law Enforcement Community and to uphold the public trust, the American Association of Police Polygraphists will support only those methods of truth verification or lie detection which are supported by valid scientific evidence.

At issue is whether or not scientific research has demonstrated the validity and reliability of the voice stress equipment, now commonly referred to as computerized voice stress analysers (CVSA). To date, the AAPP has found no scientific studies or independent research which support voice stress analysis as a method of discriminating between truth and deception. In fact, the most recent study by the Department of Defence, completed in September 1996, concluded that there was “no credible evidence to validate voice analysis as an effective instrument for determining deception.

Ultimately, every procedure and process employed by a law enforcement agency must be able to withstand the in-depth scrutiny of judicial proceedings. In making a determination of acceptability, the courts will weigh the available scientific data. “Testimonials” without the support of reliable scientific (information will not meet the standards for acceptable evidence. Polygraph is the only deception detection device which has the scientific support and has earned judicial acceptance for expert testimony.

In addition to jeopardizing criminal proceedings, the use of methods and equipment which have not been proven to be impartial, valid and reliable may expose a law enforcement agency to potential civil liability. As law enforcement professionals and public servants, it is our duty and responsibility to protect and uphold the individual civil rights of the citizens which we serve.

The AAPP joins with other professional national and state polygraph associations which require their members to utilize proven professional procedures and instrumentation. Until voice stress analysis is supported by scientific research that conclusively demonstrates its validity and reliability, the American Association of Police Polygraphists will not endorse the use of such equipment in the law enforcement community.