FIG. 4.—The psychographs of three school girls, showing their standings in various mental functions, measured to determine mathematical ability; illustrating use of the vertical line to denote typical performance. The scores are in terms of weighted deviations. Scores to the right are above, and scores to the left are below, average. (From _Tests of Mathematical Ability and Their Prognostic Value_. Reproduced by courtesy of Agnes L. Rogers.) ] Figure 4 shows the use of the vertical line as the “type” or “norm,” picturing the extent to which the individual measured departs from or corresponds to the typical, in the functions tested. Figure 5 illustrates the use of the circle, with radii to show standing in the various mental functions. The adolescent presented is near the typical (the 50 percentile) in nearly all functions measured. Which of these forms of graph is best adapted to its purpose has not been determined. All are simply different methods of picturing the same facts. The chief obstacle to the platting of psychographs, for such capacities as are now measurable, is that scales for measurement have been standardized in different terms. To plat a lucid psychograph, some traits on which have been measured in P.E., some in IQ, some in percentiles, some in “raw” points, some in values of a T Scale, some in terms of school grade achieved[7] is now impossible, because of the difficulties of equating all these “steps” of difference. The psychographs here presented will, therefore, be understood to be crude, merely approximating the lucidity of those which will be made in future, when the science of mental measurement has made greater progress. Each of the methods of standardization has some advantages and some disadvantages, as compared with the others. Only experience and discussion can finally determine which is best. It is desirable to achieve uniformity as soon as possible, in order that the psychographic study of individuals may be facilitated. [Illustration: 1. General Intelligence (Stanford-Binet) 2. Completion Test (Trabue) 3. Cancellation (Pinter) 4. Digit Symbol (Pinter) 5. Opposites (Pinter) 6. Mechanical Ability (Stenquist) 7. Tonal Memory (Seashore) 8. Pitch (Seashore) 9. Time (Seashore) 10. Intensity (Seashore) 11. Pictoral Completion (Healy) 12. Grip in Hand (Smedley) FIG. 5.—The psychograph of a school boy, showing his standing in various mental functions; illustrating use of the circle as a diagram, the median circumference denoting the performance of typical persons of his age. The scores are in terms of percentiles. ] XII. AT WHAT AGE IS MENTAL ENDOWMENT EVIDENT?