These included sampling error, differences in the populations from which subjects were drawn (subjects), differences in the nature of incentives provided to subjects for passing the polygraph test (incentives), and differences in the methods for diagnosing truth or deception (decision policy). A meta-analysis revealed that approximately 24 percent of the variance in detection rates could be attributed to sampling error, and detection rates were correlated with types of subjects (r=.61), incentives (r=.73), and decision policies (r=.67). The highest diagnostic accuracies were obtained from nonstudent subject samples when both guilty and innocent subjects were offered monetary incentives to convince the examiner of their innocence, and when conventional field methods were used for interpreting the physiological recordings and diagnosing truth and deception. Together, differences in subjects, incentives, and decision policies may account for as much as 65 percent of the observed variance in detection rates. The present findings highlight the importance of conducting mock crime experiments that closely approximate field conditions. 3 tables and 34 references. (Author abstract modified)