1. Preliminary trial designated 1st trial 2. Median of first 5 trials designated 5th trial 3. Median of trials 20 to 25 designated 25th trial 4. Median of trials 75 to 80 designated 80th trial 5. Median of trials 200 to 205 designated 205th trial At each of these points the thirteen individuals were arranged in an order of relative ability for each of the tests, and these orders were correlated with each other. Table 23 gives, for each test, at each point, the average correlation with all the other tests, and also the grand average correlations of all tests. TABLE 23 SHOWING THE AVERAGE CORRELATION OF EACH TEST WITH ALL OTHERS, AT VARIOUS POINTS IN THE CURVE OF PRACTICE -------------------------------------------------------------- Trial|Adding|Opposites| Color|Discrim-|Coordi-|Tapping| Final | | |Naming| ination| nation| |Average -----+------+---------+------+--------+-------+-------+------- 1 | .19 | .10 | .15 | -.07 | -.15 | .17 | .065 5 | .41 | .26 | .15 | .35 | .21 | .32 | .280 25 | .50 | .35 | .43 | .27 | .03 | .35 | .320 80 | .55 | .43 | .53 | .31 | .18 | .34 | .390 205 | .48 | .62 | .61 | .35 | .34 | .52 | .490 -------------------------------------------------------------- Except in the case of discrimination the effect of practice is to increase to a marked degree the intercorrelations of the various tests. Adding increases steadily up to the eightieth trial. Opposites and color naming gain even more steadily to the very end of the experiment, the increase in the coefficients being four to six fold. Tapping increases more slowly but no less certainly. In coordination the increase is very irregular, but the coefficients show, on the whole, a change from -.15 at the first trial to .34 at the finish. Only in the case of discrimination is there failure to increase after the fifth trial. In no case, after the preliminary trial, is there a negative coefficient among the average correlations, and indeed in only one case is there a coefficient smaller than .15. The final averages show steady increase from .065 at the preliminary to .28 at the fifth, .32 at the twenty-fifth, .39 at the eightieth, and .49 at the two-hundred-and-fifth trials. _With practice, then, the average correlations of all tests become positive, and the coefficients become greater the longer the practice is continued._ In producing this increase in the intercorrelation of specific abilities through the medium of practice, at least three different factors probably cooperate. These factors have not an equal significance for vocational psychology and its interests in tests.