New Ratios for Scoring Electrodermal Responses

• NCJ Number: 215329
• Journal: Polygraph Volume: 35 Issue: 2 Dated: 2006 Pages: 65-70
• Author(s): Donald J. Krapohl; Mark D. Handler
• Date Published: 2006
• Length: 6 pages
• Publication Format: Article
• Publication Type: Test/Measurement; Report (Study/Research)
• Language: English
• Country: United States of America

Annotation

This study compared the traditional method of scoring the electrodermal response (EDR) in a polygraph exam with a new scoring system that uses a different ratio scheme.

Abstract

The traditional method of analyzing the electrodermal channel in a polygraph exam is to compare the response from the relevant question with that of the comparison question by assigning scores based on their relative magnitudes. In the traditional 7-position scoring systems, threshold ratios of 2:1, 3:1, and 4:1 are used for the assignment of scores +/-1, +/-2, and +/-3, respectively. Based on previous research, there is evidence that these ratios are too conservative and that lower ratios could produce additional diagnostic value from the electrodermal channel beyond that yielded by traditional ratios. In both automated and manual conditions, this study found that a new ratio scheme of 1.25:1, 2:1, and 3:1 captured more diagnostic information than the traditional ratios. This conclusion was drawn because the average scores of the deceptive and nondeceptive cases were further from each other under the new threshold ratios than under the traditional threshold ratios. Despite the better scores under the new ratios, however, decision improvement was not statistically significant. Since this is the first study of the new ratios, further research is required to confirm that the new ratios can improve the analysis of polygraph exams. Under the automated condition, 150 truthful and 150 deceptive cases were used. All cases were conducted with the Federal Zone Comparison Technique, and each case had three charts and three relevant questions. Under the manual condition, 100 cases were drawn from a database of confirmed cases, with half being deceptive. They were analyzed by polygraph examiners undergoing competency certification under the Marin Protocol. All cases were conducted with the Federal Zone Comparison Technique. 2 tables, 3 figures, and 8 references