of comparison, the location of these designs on a P. E. Scale, the derivation of which is explained in the division on "P. E. Scale Norms."1

1 1It should be noted that although the original time limits for each design were somewhat longer than the later revision, the revision itself covers practically the same amount of time in which success may reasonably be expected. The validity of the above-indicated norms are, therefore, in no way affected by this change.

(a) Method

3. P. E. STANDARDIZATION

For a full and detailed explanation of the principles underlying the scaling of tests on a P. E. basis and for the technique involved, the reader is referred to the work of Buckingham, Trabue, and Woody. Here, let it suffice to mention that by means of this method, each test in the series is weighted, first, depending on the P. E. intervals between the separate ages, and second, depending on the ratios between the number of passes and failures. In Table L are presented the per cents passing each design at the various ages from 3 to 19. (This data is based on the age norms, mental and chronological, smoothed.) In Table LI are presented the differences between 50 per cent and the per cent passing a design at each age. The data are thus prepared for the use of Sheppard's Tables,1 and in Table LII are accordingly presented the P. E. equivalents of the items in Table LI. In Table LIII are presented the P. E. intervals between consecutive ages, the bottom of the table showing the average intervals between consecutive ages. In Table LIV are tabulated the distances of each age median above the zero of the P. E. scale. The separate agedistributions are presented graphically in Graph 40.

It should be stated that a few minor modifications have been made in the application of this method to our problem. These changes have been in the direction of eliminating some of the super-refinements. In theory and result the method has been kept intact

1 See Appendix III.