The Measurement of Intelligence. Lewis M. Terman

affect mental development unfavorably; but as long as these influences have not been sifted, weighed, and measured, we have nothing but conjecture on which to base our efforts in this direction.

      When we search the literature of child hygiene for reliable evidence as to the injurious effects upon mental ability of malnutrition, decayed teeth, obstructed breathing, reduced sleep, bad ventilation, insufficient exercise, etc., we are met by endless assertion painfully unsupported by demonstrated fact. We have, indeed, very little exact knowledge regarding the mental effects of any of the factors just mentioned. When standardized mental tests have come into more general use, such influences will be easy to detect wherever they are really present.

      Again, the most important question of heredity is that regarding the inheritance of intelligence; but this is a problem which cannot be attacked at all without some accurate means of identifying the thing which is the object of study. Without the use of scales for measuring intelligence we can give no better answer as to the essential difference between a genius and a fool than is to be found in legend and fiction.

      Applying this to school children, it means that without such tests we cannot know to what extent a child’s mental performances are determined by environment and to what extent by heredity. Is the place of the so-called lower classes in the social and industrial scale the result of their inferior native endowment, or is their apparent inferiority merely a result of their inferior home and school training? Is genius more common among children of the educated classes than among the children of the ignorant and poor? Are the inferior races really inferior, or are they merely unfortunate in their lack of opportunity to learn?

      Only intelligence tests can answer these questions and grade the raw material with which education works. Without them we can never distinguish the results of our educational efforts with a given child from the influence of the child’s original endowment. Such tests would have told us, for example, whether the much-discussed “wonder children,” such as the Sidis and Wiener boys and the Stoner girl, owe their precocious intellectual prowess to superior training (as their parents believe) or to superior native ability. The supposed effects upon mental development of new methods of mind training, which are exploited so confidently from time to time (e.g., the Montessori method and the various systems of sensory and motor training for the feeble-minded), will have to be checked up by the same kind of scientific measurement.

      In all these fields intelligence tests are certain to play an ever-increasing rôle. With the exception of moral character there is nothing as significant for a child’s future as his grade of intelligence. Even health itself is likely to have less influence in determining success in life. Although strength and swiftness have always had great survival value among the lower animals, these characteristics have long since lost their supremacy in man’s struggle for existence. For us the rule of brawn has been broken, and intelligence has become the decisive factor in success. Schools, railroads, factories, and the largest commercial concerns may be successfully managed by persons who are physically weak or even sickly. One who has intelligence constantly measures opportunities against his own strength or weakness and adjusts himself to conditions by following those leads which promise most toward the realization of his individual possibilities.

      All classes of intellects, the weakest as well as the strongest, will profit by the application of their talents to tasks which are consonant with their ability. When we have learned the lessons which intelligence tests have to teach, we shall no longer blame mentally defective workmen for their industrial inefficiency, punish weak-minded children because of their inability to learn, or imprison and hang mentally defective criminals because they lacked the intelligence to appreciate the ordinary codes of social conduct.

      FOOTNOTES:

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      [1] See References at end of volume.

      [2] H. H. Goddard: The Kallikak Family. (1914.) 141 pp.

[3] Danielson and Davenport: The Hill Folk. Eugenics Record Office, Memoir No. 1. 1912. 56 pp.

[4] Estabrook and Davenport: The Nam Family. Eugenics Record Office Memoir No. 2. (1912). 85 pp.

[5] R. L. Dugdale: The Jukes. (Fourth edition, 1910.) 120 pp. G. P. Putnam’s Sons.

[6] See p. 26 ff. for further illustrations of this kind.

CHAPTER II

       SOURCES OF ERROR IN JUDGING INTELLIGENCE

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Are intelligence tests superfluous?

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      Binet tells us that he often encountered the criticism that intelligence tests are superfluous, and that in going to so much trouble to devise his measuring scale he was forcing an open door. Those who made this criticism believed that the observant teacher or parent is able to make an offhand estimate of a child’s intelligence which is accurate enough. “It is a stupid teacher,” said one, “who needs a psychologist to tell her which pupils are not intelligent.” Every one who uses intelligence tests meets this attitude from time to time.

      This should not be surprising or discouraging. It is only natural that those who are unfamiliar with the methods of psychology should occasionally question their validity or worth, just as there are many excellent people who do not “believe in” vaccination against typhoid and small pox, operations for appendicitis, etc.

      There is an additional reason why the applications of psychology have to overcome a good deal of conservatism and skepticism; namely, the fact that every one, whether psychologically trained or not, acquires in the ordinary experiences of life a certain degree of expertness in the observation and interpretation of mental traits. The possession of this little fund of practical working knowledge makes most people slow to admit any one’s claim to greater expertness. When the astronomer tells us the distance to Jupiter, we accept his statement, because we recognize that our ordinary experience affords no basis for judgment about such matters. But every one acquires more or less facility in distinguishing the coarser differences among people in intelligence, and this half-knowledge naturally generates a certain amount of resistance to the more refined method of tests.

      It should be evident, however, that we need more than the ability merely to distinguish a genius from a simpleton, just as a physician needs something more than the ability to distinguish an athlete from a man dying of consumption. It is necessary to have a definite and accurate diagnosis, one which will differentiate more finely the many degrees and qualities of intelligence. Just as in the case of physical illness, we need to know not merely that the patient is sick, but also why he is sick, what organs are involved, what course the illness will run, and what physical work the patient can safely undertake, so in the case of a retarded child, we need to know the exact degree of intellectual deficiency, what mental functions are chiefly concerned in the defect, whether the deficiency is due to innate endowment, to physical illness, or to faults of education, and what lines of mental activity the child will be