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GAINES, K. H. Utility and numerical evaluation of the guilty knowledge test. August 1992, Report No. DoDPI92-R-0004. Department of Defense Polygraph Institute, Ft. McClellan, AL 36205.

Eighty subjects were given polygraph examinations utilizing the Guilty Knowledge Test (GKT) in an effort to test the utility of that procedure in a mock crime situation. Additionally, a semi-objective numerical scoring system was implemented, modified, and evaluated. The subjects were broken down into two equal groups. The first group was programmed to commit the mock crime (a burglary/homicide). The second group did not commit the mock crime and was given no information regarding the details of the crime. Half the sample (twenty innocent and twenty guilty), was utilized to design the scoring system. It was then tested on the remaining half. The GKT with the developed numerical scoring system correctly identified fifteen of twenty programmed guilty subjects and seventeen of twenty programmed innocent subjects, with one inconclusive decision. The overall accuracy rate was 82%.

Key-words: guilty knowledge, psychophysiological detection of deception, PDD examiners, GKT

Director's Foreword

This research examined nine approaches of scoring the guilty knowledge test (GKT) format, a methodology preferred by some scientists. The most commonly used analytic technique was less accurate than a procedure devised as a result of this research. Although the GKT and related peak of tension test formats are not widely used in criminal investigations, when they are used, the optimum scoring system should be applied.

The results of this study suggest that an attempt to replicate it with confirmed GKT tests from the field should be undertaken. This is not a high priority project for DoDPI due to the limited use of the GKT in the field.

Michael H. Capps