In a recent paper by Meehl and Rosen (1955) several important criticisms are made against the majority of diagnostic psychological instruments reported in the literature. Some of these criticisms are well known, for example absence of cross-validation data, not stating the type of population most suited for the particular psychometric device, etc. The main purpose of the present paper is to try to meet, with respect to the M.W.-L.T. (Walton and Black, 1957), one of their other major criticisms namely, that “Base rates are virtually never reported. It is, therefore, difficult to determine whether or not a given device results in a greater number of correct decisions than would be possible solely on the basis of the rates from previous experience. When, however, the base rates can be estimated, the reported claims of efficiency of psychometric instruments are often seen to be without foundation.”