At each of these points the thirteen subjects were arranged in order of relative ability for the test at the given stage of practice. Each of these orders, or cross sections, of the group of practice curves was then correlated with the final order of position as shown in trials one hundred and seventy to one hundred and seventy-five. Table 24 gives the coefficients of correlation derived in this way. A careful study of this table will prove instructive.

TABLE 24

Showing the Correlation of Ultimate Capacity with Capacity at Different Points in the Curve of Learning

(See Text for Explanation)

The TestPreliminary 5th Trial 25th Trial 50th Trial 80th Trial 130th TrialFinal Trial 175th
Adding .15 .19 .87 .87 .97 .96 1.00
Opposites -.08 .62 .49 .83 .94 .98 1.00
Color Naming .68 .89 .86 .91 .97 .97 1.00
Discrimination .68 .62 .60 .50 .50 .79 1.00
Cancellation .67 .68 .88 .69 .93(1.00) —
Coördination .52 .79 .77 .90 .95(1.00) —
Tapping .23 .48 .63 .68 .69 .89 1.00
Averages .41 .61 .73 .77 .85 .92 1.00

It is at once evident that the preliminary trial is by no means always a measure of the final relative capacities of the individuals tested. The average of all seven coefficients increases from .41 at the preliminary trial to .92 at the one hundred and thirtieth trial. As the trials proceed then, the relative positions of the thirteen individuals become more and more definitely fixed, but in the beginning the indication is obscure. The rate of this process, however, varies with the test, and to a considerable degree. Adding shows changes in position which effect a correlation of .87 only after the twenty-fifth trial. Beyond this point there is little change, the eightieth and one hundred and thirtieth trials correlating equally well, and practically perfectly, with the final order. After twenty-five trials, then, the final capacities of the individuals in the adding test may be said to be indicated fairly accurately. Opposites, in the fiftieth trial, yields a coefficient equal to that of addition in the twenty-fifth trial, and by the eightieth trial the correlation may be said to be complete. Only after fifty trials, then, can the test be said to yield comparative measures which reflect the individual's final capacity in this form of controlled association. In the case of tapping it is only at the one hundred and thirtieth trial that the correlation with final position exceeds .69.

These results may be easily comprehended by thinking of each test (as for instance the tapping test) as a prolonged race, consisting of a large number of heats (205 separate trials). All individuals begin with a running start, their respective initial speeds depending on the momentum they have acquired through a certain amount of previous practice, and on such momentary ability and zeal as they possess at the time. But as the succeeding "heats" or trials occur some individuals who were originally in the lead begin to lose ground in relation to others who, though initially slower, are now speeding up and overtaking the leaders. Still others may retain their original relative positions to the end of the race. In the table of coefficients, a correlation of 1.00 indicates that at that point the ultimate relative positions of the contestants have at last become established. The nearer the figure approaches zero the more uncertain are the relative positions at the particular trial. To terminate the race at a point where the correlation is low and to reward the contestants according to the position they had reached at that point would be manifestly unfair to those who were still speeding up and partial to those who were losing ground.

Color-naming, discrimination, cancellation, and coördination show up to much greater advantage. Even the preliminary trials in these tests show fairly high correlations with the final orders. The first two of these show little change as practice proceeds. In the case of the latter two tests, although the initial correlations are fairly high, there is nevertheless considerable increase as the trials proceed.

The meaning of these results seems to be that before one attempts to interpret individual differences as disclosed by performance in such a series of simple tests, he should have clearly in mind the distinction between temporary proficiency and ultimate capacity. If he is interested, for example, in determining the vocational prospects of a youth, or the relative merits of candidates or culprits, it is important that he realize that relative abilities in many of these laboratory tests may be changed quite beyond recognition by continued work. It is highly desirable to know more than we now know concerning the degree to which initial and intermediate trials in these tests reflect final capacity. In the past the question seems hardly to have been asked. Individual differences in early trials, in some tests, are fairly significant of the working level to which the performer may be brought later. In other tests this is not the case. On the significance of these early trials may depend, in many cases, the vocational value of the particular test.

Changes in the nature of the tests, variations of methods of attack, and specific improvement in the directness, independence and rapidity of the special nervous connections concerned—these three factors would all declare themselves in the form of "changes in ability." A useful piece of work in the case of all tests will be the analysis of the nature of the changes resulting from practice. But in any case the presence of these changes in correlation shows that we are not, in early trials, measuring the same tendency or capacity in all performers. The concrete tasks of daily life doubtless show just such qualitative changes, during practice, as we may suppose to be present in some of these tests. Just as it is ultimate capacity in daily life that is, with a given set of incentives, most important, so in the laboratory the measurement of "ability after practice" ought to be more emphasized than it is at present.