Part 13 (1/2)
One of the least important of these factors is the variability of individual performance. In the beginning of the experiment each individual is more variable than at later points in the curve. This momentary variability need not be supposed to affect all the tests in the same way nor all individuals in the same direction. This fact may then tend somewhat to reduce the correlation of the preliminary trials and may in some cases materially affect the first five or ten trials. Beyond the twenty-fifth trial the variability in these tests is much reduced, and particularly so in the measures here used, which are in all cases, after the preliminary trial, the medians of five successive trials.
Another factor that deserves mention is the possibility of change in the character of the tests themselves, through practice with them. It is quite probable, for example, that the opposites test comes, after many repet.i.tions, to resemble more and more that type of process or function involved in color-naming. The responses become more and more intimately a.s.sociated with the stimulus words, the suggested responses to each word become more and more limited in number and in most cases reduced to a single word for each stimulus. This state of affairs is true of color-naming at the very beginning of the experiment. As the order of the stimulus words is changed at each trial, the test may come to involve more and more the simple task of giving merely the quickest possible a.s.sociation of the right response, and the overcoming of inhibitions and interferences of a more or less general sort, with less and less emphasis on the element of selection. Much the same may also be true of the addition test. It is in these three tests that the increase in correlation is most marked, and the actual coefficients highest at the end of the experiment. Careful a.n.a.lysis of what takes place as one improves in these simple tests would no doubt yield interesting material.
But these two factors--decrease in variability and change in the character of the tests--seem to be far from sufficient to account for the results.
The tapping test remains much the same type of process throughout, the only apparent modifications consisting of slight changes in method and perhaps some gradual changes in the muscles. There is certainly no reason for suspecting that tapping and opposites or tapping and discrimination become, as tests, more alike because of frequent repet.i.tion. But the increase in correlation is clear in both these cases. Again, it is well established that the discrimination reaction, in the form here used, also tends to become reflex through practice, the conscious discrimination coming only after the correct reaction is made. These experiments called for between 3,075 and 4,100 single discrimination reactions on the part of each observer, which would afford ample time for such a change to show itself.
Mere change in the character of the test would then lead us to expect color-naming, opposites, and adding to come more and more to resemble discrimination reaction. But they do not, if the coefficients may be taken as evidence. The coefficients of these tests with discrimination show no tendency to increase, even by the end of the experiment. The a.s.sumption of increasing similarity in the character of these pairs of tests would seem gratuitous. Moreover, if there were such increase in similarity, and this be also supposed to account for the higher correlation of color-naming and opposites with adding, coordination and adding should show the same increase in correlation. Just the reverse is actually the case, the correlation of coordination and adding decreasing consistently.
Some further factor must then be responsible for the general increase in correlation, aside from decrease in variability (which affects only the first few trials) and progressive qualitative approximation of the tests (which is seen to be inadequate). The doctrine of ”general ability” or ”general intelligence” at once suggests itself in this connection. If there is such a thing as ”general ability” or ”general intelligence,” we should expect all samplings of that ability to correlate more and more as the measures came to be truer samples. We might indeed expect to find evidences of this general ability only when measuring the ”ultimate capacity” of the individuals concerned. The momentary ability revealed in initial trials, or even in the first half-dozen trials, in a given set of tests might well be expected to show only low degrees of correlation. These trials would not be measures of ultimate capacity, but would be largely determined by previous practice, chance variability, momentary att.i.tude and initial method of attack. They would, in short, be samplings only of momentary ability, not of final capacity.
Or if the a.s.sumption of a common factor be rejected, the present evidence tends strongly to support our earlier conclusion concerning the positive correlation between desirable mental functions. Some form of the doctrine of ”general ability,” at any rate, seems to be supported. But the conclusion seems to call for the qualification that ”general ability” shall have reference to _final capacity_ rather than to _momentary performance_, if the correlations are to be high. If each individual be given the opportunity to attain his limit of efficiency, his highest level of performance, then, when these final limits are reached, individuals who excel their fellows in one type of work will also tend to excel in other types of work.
The theory and practice of tests has in the past been too content to rest its claims on the meager results of a few preliminary samplings of an individual's ability. The fact that, even when a great variety of such samplings of a given individual are aggregated and balanced off against one another, few results of real diagnostic value are achieved should be sufficient warning against this tendency. My conviction is that for this purpose we shall find it necessary to determine the individual's ”limit of practice” in the various tests before we shall secure diagnostic results which will be verified by the individual's subsequent achievement in daily life. We should know much more than we now know concerning the tendency and meaning of such correlations as show close relation between initial performance and ultimate capacity. This is particularly true if we wish to extend the method of tests beyond educational diagnosis and to use them as a means of vocational guidance or of industrial selection. For educational diagnosis we wish primarily to know what kind of practice the individual most needs. For vocational and industrial purposes we need rather to know what limits the individual can eventually reach, in given kinds of performance, as the result of practice, and to what degree his present equipment of incentive renders probable the actual achievement of this limit.
On the question of the significance of preliminary trials and the effects of practice on the relative standing of individuals in their group, there are important facts to be considered. In the direct application of mental tests it has too often been a.s.sumed that the actual performance of an individual, in one or a dozen trials at a given task, is in some way or other significant of that individual's final capacity in such work. It is true that several investigators have studied the effects of practice on individual differences. These workers were interested above all in questions as to relative rate of improvement, or amount or permanence of gain. Such studies have produced suggestive results, although they have been based, for the most part, on records of only a few subjects or on relatively few practice trials.
To what degree are individual differences after a given number of trials indicative of the final maximum capacity of the individuals concerned? At what various rates do the determining factors enter into the practice curves of a group of workers? What manner and amount of displacement in their relative order of ability are thus produced? At what point or points in the curves do the individuals a.s.sume their final order of relative capacity after training? How do the replies to these questions vary with the character of the task?
In the case of the experiments already described, record has been here taken of the following points in the curves of practice:
Preliminary trial called initial trial Median of trials 1 to 5 called 5th trial Median of trials 20 to 25 called 25th trial Median of trials 46 to 50 called 50th trial Median of trials 76 to 80 called 80th trial Median of trials 126 to 130 called 130th trial Median of trials 171 to 175 called 175th trial
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)
-----------------------------------------------------------
Final The Test
Prelim-
5th
25th
50th
80th
130th
Trial
inary
Trial
Trial
Trial
Trial
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