The Diagnostic .Fallibility of Intelligence Ratios

The Diagnostic .Fallibility of Intelligence Ratios

L ~~ Qr5L • THE DIAGNOSTIC .FALLIBILITY OF INTELLIGENCE RATIOS BY FLORENCE MATEER, Ph. D. Psycho-Clinician, Ohio Bureau of Juvenile Research Reprinted from THE PEDAGOGICAL SEMINARY December, 1918, Vol. XXV, pp. 369-392 THE DIAGNOSTIC FALLIBILITY OF INTELLI­ GENCE RATIOS* By FLORENCE MATEER, Ph. D., Psycho-Clin ic ian, Ohio Bureau of Juvenile Research T he use of intelligence ratios as an aid in the diagnosis of feeble-mindedness is the outgrowth of a very recent statistical trend in clinical psychology. Just how far this usage may extend one can hardly predict, but a brief exposition of the fallacies involved in any such procedure is surely timely and necessary in the interest of the individual who is diagnosed by such a method. It is also advisable for the protection of social agencies which have to deal with children who have been so di agnosed. vVhen tests evaluating mentality in terms of mental age were first adopted the ordinary procedure was to determine the child's mental age, compare it with his actual chronological age, and thus ascertain the amount of mental retardation or acceleration, expressed in terms of years of mentality. Over two years of retardation was considered as evidence of feeble­ mindedness when the child examined was actually less than nine chronologically. Over three years of retardation was accepted as equally significant in a child over nine years of age. Binet ( 1) , himself, presented this method. He defined idiocy as development corresponding to that of birth to 2 / years, imbecility as equal to 2 to 7 years of development, and moronity as beginning at the mental age of 8. He does not define the upper limits of moronity in terms of years, but says it lies below the upper limit of his 1908 scale. No child would, however, be placed in any one of these classified groups unless he were definitely feeble-minded and tested at least two or three years below age. Even then, Binet ( 1) writes: " It is understood that these diagnoses apply only to the present moment. One who is imbecile today may, by the progress of age, become a moron, or on the contrary remain an imbecile all hi s life. One knows nothing of that; the prognosis is reserved " ( p. 270). Goddard ( 5) defines the usage of the mental age in similar but much more definite terms, writing, "It has been found that if a child is more than two years * Study made while psychologist, Massachusetts School for the Feeble-Minded, Waverley, Mass. 369 370 DIAGNOSTIC FALLIBILITY OF INTELLIGENCE RATIOS backward while he is still under nine years of age, he is prob­ ably feeble-minded. For a child above nine, we allo!'f him more than three years backward before we call him defective " (p. 86) . At first conservative usage generally intetpreted this to mean that four years of retardation were equivalent to feeble-mindedness. Goddard ( 7), also, uses it in this fashion in estimating the percentage of feeble-minded children found in testing an unselected group of public school children. These two ways of stating the same thing have, however, led to some confusion in the interpretation of various authors where the exact usage is not always stated. It will be seen from the above statements from Goddard and Binet that the usage of a mental age without reference to the subject's actual age is not to be condoned, while diag­ nosis depends not only upon the relativity of the two but also upon the actual chronological age at which such a ratio of mental and chronological age occurs. Gradually during the last five years there has appeared a tendency to disregard this last factor of the actual age of the child at the time of examination and to classify him diag­ nostically by the use of some ratio expressing the comparison of his mental and chronological ages. Intelligence quotients, mental quotients, coefficients of intellectual ability, and even " absolute " intelligence ratios have been suggested. To one who is practically engaged in clinical work all of these modi­ fications seem to be an outgrowth of a feeling that the tests are non-diagnostic, or rather that they are not sufficiently so. Each suggestion that findings be treated in this or that way indicates another attempt to make the tests express infallibly and in careful decimal fashion not only differential diagnoses but also prognoses. · Binet saw this difficulty and emphatically stated that the tests are by no means a substitute for the expert in the study of children. He also states that the test level is diagnostic and that " prognosis is reserved," but few of our American writers seem to see the relation of his clear statements, based upon the experience of evolving the scale, to their use of it in clinical fashion. A mental test by any one test series has, presumably, as one of its immediate purposes, the ascertainment of a mental age. If this mental age be translated into a decimal of the amount the child should do, it becomes what Yerkes terms an intelli­ gence coefficient ; if it be translated into a decimal indicating his mental age in relation to his chronological age, it becomes what Terman calls an intelligence quotient and what Stern termed a mental quotient. Otis goes even farther and would attempt to ascertain a child's absolute grade of brightness, DIAGNOSTIC FALLIBILITY OF INTELLIGENCE RATIOS 371 compare it with the absolute grade of brightness for his age, and thus obtain an " absolute " intelligence quotient which would, theoretically, enable us to "predict the probable maxi­ mum intellectual attainments which he will achieve" (2, p. 140) . The use of any of these ratios, or of the consideration of mental age in relation to chronological age, may then serve two purposes. It may, first of all, classify a child with others of a group doing a similar proportion of normal requirements. In this sense it is diagnostic of present mental level. It is sometimes used to indicate the child's probable future devel­ opment and in this case it is prognostic. The simplicity of classification by any of the various scales has led to a very general acceptance of the attitude that this differentiation of prognosis and diagnosis is unnecessary, that the two are iden­ tical. A child tests at age on the scale now; he is therefore " normal " and will remain " normal." The first application of the term "normal" is diagnostic of the child's present level compared with the level of other children of similar age. The second usage of the term is the result of the inference that once normal always normal. The term implies that, and the inference would be correct were our first diagnostic state­ ment based upon an absolute knowledge of normality. In­ stead it is based upon a very poorly standardized group of "averages." This prognostic usage is also encouraged by the fact that a classification of any child as feeble-minded has embodied in it the actual prognosis. But even this interpre­ tation is not infallible. The child who tests at age may be normal, defective or psychotic. The child who is more than three years retarded is surely not normal but he may be de­ mented or feeble-minded, or both. The mental age in the second case removes one possibility, that of normality or average endowment, but it leaves three other possible condi­ tions which differ greatly but which no mental age, coefficient, or intelligence quotient, taken alone, can indicate. So far the possibility that the child whose mental age indicates abnor­ mality is insane or a predementia seems to have been almost entirely overlooked. Diagnosis, prognosis included, has been made quantitatively, irrespective of quality of responses. This practice has led to some most conflicting statements regarding mental tests and their application, all of which cannot be true. Stern ( 12) was one of the first to propose the use of a ratio for diagnostic purposes. He found years of retardation difficult to handle because the number of years of retardation was different for children of different ages where the mentali­ ties might be the same. He consequently proposed the " men­ tal quotient " or the ratio of the mental age to the actual or 372 DIAGNOSTIC FALLIBILITY OF INTELLIGENCE RATIOS chronological age. He defines as feeble-minded all those with quotients below .80. He does not find the quotient entirely satisfactory, however, as it fluctuates on growing children, varying even in the individual from time to time. The suggestion was nevertheless taken up in this country and has been much in favor with two groups of workers, best represented by their respective leaders, Yerkes and Terman. Yerkes devised the coefficient of intellectual ability, or the number of points a person scores on the Point Scale, divided by the number of points a person of his age should soore. He, too, finds that there is a great deal of fluctuation in such a ratio ( 17 ), and that it is consequently not wholly reliable. He gives a tentative classification for its use, despite this un­ reliability, calling those dependent who have a coefficient of ~SO or less ; those inferior who range from .51 to .70; those subnormal who have a coefficient of .71 to .90. Haines (8), Rossy, and others uphold the use of this method or of some modification of it. Kuhlmann (9) was probably the first man in this country to advocate the use of some such quotient but hi s work received very little recognition untii taken up by Terman ( 15 ) and employed as an integral part of the Stan­ ford Revision of the Binet-Simon Scale.

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