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Utah Numerical Scoring System

NCJ Number
Polygraph Volume: 28 Issue: 1 Dated: 1999 Pages: 1-9
Date Published
9 pages

This report describes and assesses the Utah method for numerically evaluating polygraph charts from specific-incident, comparison-question tests.


Under this method, a score from +3 to -3 is assigned for respiration, electrodermal activity (skin conductance or skin resistance), relative blood pressure (cardiograph), and peripheral vasomotor activity (finger plethysmograph) for each presentation of a relevant question. The reaction to the relevant question is compared to the reaction to a nearby comparison (control) question. A positive score is assigned when the psychophysiological reaction to the comparison question is greater than to the relevant question; a negative score is assigned when the reaction to the relevant question is greater; and a zero is assigned when the responses to the relevant and comparison questions are approximately equal. Scores are based on the criteria described in this report. The reliability of the Utah scoring system has been evaluated in several laboratory experiments at the University of Utah. On average, the interrater reliability of the Utah system exceeded .90, as measured by the correlations between total numerical scores assigned by two or more evaluators. The percent agreement on decisions exceeded 95 percent when both numerical evaluators reached a definite decision. Similar reliabilities between raters who use the Utah system have been obtained in field studies. The validity of the Utah system has also been established. This report presents decision accuracies from several laboratory experiments. Excluding inconclusive outcomes, the overall percentage of correct decisions was 91 percent for guilty subjects and 89 percent for innocent subjects. Common artifacts that may affect numerical evaluations are discussed, as are limitations of the Utah scoring system. 2 tables, 1 figure, and 15 references

Date Published: January 1, 1999