The reliability of a criterion referenced test was defined as a measure of the degree to which the test discriminates between an individual's level of performance and a predetermined criterion level. The variances of observed and true scores were defined as the squared deviation of the score from the criterion. Based on these definitions and the model of a score on a criterion referenced test, criterion referenced reliability was defined by analogy to norm referenced test theory as the proportion of observed variance attributable to true variance. Error variance was then defined in terms of the binomial distribution, and a calculation formula for the criterion referenced reliability coefficient was developed, which was then illustrated with hypothetical data. (Author)