Very grave errors creep into a rating of efficiency where the ratings are made by different supervisors, each supervisor rating only a few men. Even where a detailed schedule of qualities is listed, each to be given a definite weight or importance in making up the total rating, as in the Army Rating Scale, the degree of ability which one man’s experience leads him to call “Average” will call forth a rating of “Superior” from another equally able supervisor whose experience has been with slightly different people. If individuals A, B, and C are rated by the first supervisor and individuals D, E, and F by the second, it is not at all safe to assume that C is rated fairly in relation to D. Only when two individuals are rated by the same supervisors upon the same scale and under the same conditions is it legitimate or safe to assume that their relative abilities are well indicated by the ratings. Assuming that the reader has obtained a reliable order of merit for the individuals he is using as a check upon the value of the Mentimeter tests, no test should be considered useful which does not result in approximately this same order of merit. The tests are, of course, so short and so crude that it is not to be expected that any test will, except by chance, show exactly the same order of ability as the production records or supervisor’s ratings furnish, but some tests will show much closer correspondence than others. Those tests which correspond most closely should be employed, while those tests which do not correspond at all should not be employed, regardless of any statement of the authors or any preconceived ideas of the reader as to what tests ought to foretell ability in any particular line of work. The proof of a test or of any method of prognostication lies in the degree to which it actually arranges people in the order of their relative efficiency in the tasks for which one seeks to foretell success. A mere glance at a record such as that shown below for twenty-eight sixth-grade pupils would show that there was a real relationship between the scholarship marks, the teacher’s estimate of intelligence, and the results of educational measurements taken by an outsider. SCORES AND RATINGS OF SIXTH-GRADE CLASS