Mean Cost Rating (MCR) has been used extensively in criminology to measure the power of prediction instruments by contrasting the concepts of cost and utility. MCR was used in connection with the criteria according to which parole boards select prospective parolees. This study shows the calculations used to indicate the significance of the degree of association between MCR and Kendall's rank correlation coefficient tau as a measure of the probability of success or failure of offenders to be paroled, based on the offenders' background characteristics and previous record of reconviction. In addition to research conducted in England, references is made to the 1974 Parole Decisionmaking Project of Davis, Calif. The paper consists chiefly of statistical tables and calculations. Four references are appended.