The findings indicate that both probability analysis (PA) and the Objective Scoring System (OSS) are valid and acceptable methods for scoring polygraph data. Both methods had high percentages of correct decisions. There were no significant differences between OSS and PA in area under the receiver operating characteristic (ROC) curve for Zone Comparison Technique (ZCT) tests or Modified General Question Technique (MGQT) tests, which suggests that the two methods are comparable in terms of accuracy. Krapohl and McManus, who developed the OSS, used data collected in the field with Axciton polygraphs. Kircher and Raskin, on the other hand, based their model on data collected with scientific instruments. Classification rates could differ because of differences in instrumentation or characteristics of samples available for model development and validation. Given the similar accuracy of the two methods, the choice of scoring method will be dictated in part by software and time constraints. A total of 160 cases from the database at the Defense Academy for Credibility Assessment were used in this study. None of the cases used in the development of OSS or PA were used in the current study Seventy-five cases were ZCT tests, 78 were MGQT tests, and 7 were You Phase examinations. Examinees were mostly males, ranging in age from 14 to 60; they consisted of witnesses, suspects, and victims. 5 tables and 5 references