«

»

Dec
27

Accuracy & Polygraph Examinations

Polygraph admissibilityPolygraph Examinations, (which The American Polygraph Association states an accuracy of 93-98%),
are exams in which an examiner monitors the psychophysiological responses of a subject while asking a set of test questions. This data (blood pressure, heart rate, etc.) records physiological responses to a person’s natural “fight or flight” impulses. Flight or fight is defined as an unconscious reaction to a physical or psychological threat that will automatically elicit a set of physiological changes, a spike in heart rate for example.

The word “polygraph” literally means “many writings”1.  This alludes to the various types of responses simultaneously monitored and recorded during the examination. The polygraph machine will collect physiological data from various autonomic systems in the examinee’s body and record them on either paper (analog) charts or computer systems (digital). This may involve placing rubber tubes around their chest or abdominal area to record respiratory activity (pneumograph). Small sensors may be attached to the fingers to record electrodermal activity. A blood pressure cuff or something similar may be used to record cardiovascular activity (heart rate and blood pressure), also referred to as a cardiograph.

The machine does NOT uncover lies.

The machine only records biological reactions and the examiner uses one of a variety of numeric scoring methods to evaluate the data and  evaluates the truthfulness of the person taking the exam. The American Polygraph Association By-Laws requires that all conclusions and opinions be based on a quantitative or numerical scoring system for all evidentiary examinations.

Accuracy

Most arguments for the admissibility of polygraph results to be used in court revolve around the accuracy of polygraph exams. The American Polygraph Association (APA) points out that the critics of polygraph tend to use any results that an examiner may deem as “inconclusive” as “errors”. The APA considers inconclusive data as just that, neutral, neither indicative of lying or truthfulness. For example, if a polygraph examiner gives 10 tests and finds 7 results to be “untruthful”, 1 “truthful”, and 2 “inconclusive”. One of the ‘untruthfuls’ is a false positive. Critics would find that not an margin of error of 10% but include the 2 ‘inconclusives’  for an error rate of 30%. In reality, the error rate is 10% and 2 findings were found to be indistinct enough as to not be conclusive one way or the other.

The American Polygraph Association‘s web site documents 11 studies of 1,609 field examinations with an average accuracy rate of 92% and 2,174 field examinations with an average accuracy of 98%.

Polygraph reliability and validity reviews of field studies2 conducted by Forensic Research, Inc., of Severna Park, Maryland, indicate that between 96 and 98 percent of exams correctly identified deception.3

Professional Standards

Key to polygraph research is that a number of variables can affect the accuracy of polygraph examinations. When looking for a professional polygraphist, make sure that…

  • The polygraph examiner uses an accepted testing procedure and scoring system4.
  • The polygraph examiner follows established practices to maximize accuracy and reliability. The American Polygraph Association has published standards of practice for examiners intended to limit variation in practice across examiners5.
  • The polygraph examiner is accredited and certified by the American Polygraph Association.

If you would like to discuss the professional services of a polygraph examiner, please contact The Polygraph Examiner at 1-800-497-9305.

  1. American Polygraph Association; Gannon, Beech, & Ward, 2008 []
  2. http://dpca.state.ny.us/pdfs/sopolygraphresearchbulletin3.pdf []
  3. For more information on concerns about polygraph accuracy and the quality of polygraph research, see Lykken’s Tremor in the Blood
    []
  4. Ansley, 1997 []
  5. Dutton, 2000 []