The value of the method lies both in the swiftness and the accuracy with which it works. One who knows how to apply the tests correctly and who is experienced in the psychological interpretation of responses can in forty minutes arrive at a more accurate judgment as to a subject’s intelligence than would be possible without the tests after months or even years of close observation. The reasons for this have already been set forth.[35] The difference is something like that between measuring a person’s height with a yardstick and estimating it by guess. That this is not an unfair statement of the case is well shown by the following candid confession by a psychologist who tested 200 juvenile delinquents brought before Judge Lindsey’s court:—
As a matter of interest I estimated the mental ages of 150 of my subjects before testing them. In 54 of the estimates the error was not more than one year in either direction; 70 of the subjects were estimated too high, the average error being 2 years and 7 months; 26 of the subjects were estimated too low, the average error being 2 years and 2 months. These figures would seem to imply that an estimate with nothing to support it is wholly unreliable, more especially as many of the estimates were four or five years wide of the mark.[36]
Criticisms of the Binet method have also been frequently voiced, but chiefly by persons who have had little experience with it or by those whose scientific training hardly justifies an opinion. It cannot be too strongly emphasized that eminence in law, medicine, education, or any other profession does not of itself enable any one to pass judgment on the validity of a psychological method.
Dependence of the scale’s reliability on the training of the examiner.
On this point two radically different opinions have been urged. On the one hand, some have insisted that the results of a test made by other than a thoroughly trained psychologist are absolutely worthless. At the opposite extreme are a few who seem to think that any teacher or physician can secure perfectly valid results after a few hours’ acquaintance with the tests.
The dispute is one which cannot be settled by the assertion of opinion, and, unfortunately, thoroughgoing investigations have not yet been made as to the frequency and extent of errors made by untrained or partially trained examiners. The only study of this kind which has so far been reported is the following:—[37]
Dr. Kohs gives the results of tests made by 58 inexperienced teachers who were taking a summer course in the Training School at Vineland. The class met three times a week for instruction in the use of the Binet scale. During the first week the students listened to three lectures by Dr. Goddard. The second week was given over to demonstration testing. Each student saw four children tested, and attended two discussion periods of an hour each. During the third, fourth, and fifth weeks each student tested one child per week, and observed the testing of two others. The student was allowed to carry the test through in his own way, but received criticism after it was finished. Twice a week Dr. Goddard spent an hour with the class, discussing experimental procedure. The subjects tested were feeble-minded children whose exact mental ages were already known, and for this reason it was possible to check up the accuracy of each student’s work.
Kohs’s table of results for the trial testing of the 174 children showed:—
- That 50 per cent of the work was as exact as any one in the laboratory could make it;
- That in an additional 38 per cent the results were within three fifths of a year of being exact;
- That nearly 90 per cent of the work of the summer students was sufficiently accurate for all practical purposes;
- That the records improved during the brief training so that during the third week only one test missed the real mental age by as much as a year.
Since hardly any of these students had had any previous experience with the Binet tests, Dr. Kohs seems to be entirely justified in his conclusion that it is possible, in the brief period of six weeks, to teach people to use the tests with a reasonable degree of accuracy.