Summarizing work which is part of an Army research program on Methodological Issues in the Construction of Criterion Referenced Tests, the focus of this paper is on a Bayesian model, which gives the probability of correctly classifying an examiner as a master or as a nonmaster while taking into consideration the test length and the mastery cut-off score. Bayes' Theorem is a mathematical expression which allows the combination of information about the quality of the examinee population so as to produce a probabilistic estimate of mastery for a specific examinee. This approach can give the most accurate ability estimate for each examinee by using the fewest number of test items, provided that accurate estimates of the "quality parameters" have been made. A method of estimating these parameters from commonly available information is also explained. (Author/BW)