By the use of more conservative borderlines for raising the presumption of deficiency and also by designating a doubtful position on the scale, on the plan advocated herein, it is possible to make scales for testing mental capacity more serviceable both to the clinician and to the amateur tester. The latter may use the scales for his own information or may wish to discover whether an examination by an expert in mental development is desirable, without attempting to make a diagnosis himself. The scale may thus take a place in the study of child mentality analogous to the familiar Snellen chart in the testing of vision. For every teacher familiarity with a development scale may thus become as essential and desirable as the knowledge of the chart for eye testing. It should find a place in all progressive schools which do not have the services of a clinician.
The Binet system of tests was used for obtaining new data on groups of juvenile delinquents in Minneapolis and Pittsburgh. The use of this scale, around which the discussion centers, grew out of the necessity for immediate practical results for the clinic at the Minneapolis Juvenile Court which I was called upon to serve. In 1912, when that work began, there was practically nothing approaching norms with children for any other scale of tests. Even today it is plain that there is more data available for interpreting results with the Binet scale than with any other system of tests. While my experience would make me unwilling to advocate the Binet tests as an ideal method for building up a measuring scale, I still feel that it remains the most useful method at present for discovering the fundamental symptoms of intellectual deficiency. The percentage method, here advocated, as the best way available for determining the borderlines with a scale, would be quite as serviceable, however, with any other testing system. It has been my aim to contribute to the interpretation of the results of the tests as they are, not to perfecting the arrangement or details of the separate tests.[[2]] It happens that one of the main objections which has been raised to the Binet scale, the inadequacy of its tests for the older ages, loses its force so far as the diagnosis of feeble-mindedness is concerned for those who accept the borderlines described in this paper.
Some diagnosticians may hesitate to use the Binet scale because of the criticisms it has received. Yerkes and Bridges state: “Indeed, we feel bound to say that the Binet scale has proved worse than useless in a very large number of cases” (226, p. 94). So far as this objection arises from the attempt to use the descriptions of the borderline of feeble-mindedness published with Binet scales, it will meet with a wide response. The difficulty is hardly less, as I shall show, with other scales. The definition of the borderline is certainly the vital point with any objective method for aiding diagnosis. Only by improving methods for determining the borderline can this weakness be attacked. The central contribution of this paper is directed, therefore, to this problem of the interpretation of the borderline, so that objective scales may be made more reliable for purposes of diagnosis.
In Part Two I have added an intensive discussion of the measurement of development and a comparison of the different objective methods for describing the borderline. This may well be omitted by those who are not interested in the technical aspects of these questions. To those who care only for accounts of individual lives, let me say that I am contributing nothing herein to that important field which has been covered in authoritative form by Dr. Healy ([27]) and by Dr. Goddard ([112]). They will find instead, I hope, the fascination of figures, a picture book in which probability curves take the place of photographs and biographies, in which general tendencies are evaluated and attention is focussed upon the problem of properly diagnosing deficiency and upon plans for the care of the feeble-minded, whether they be potential or actual delinquents.
[1]. Numbers in parenthesis indicate the references in the bibliography at the close of the book.
[2]. Those concerned with other features of the Binet scale will find an admirable bibliography by Samuel C. Kohs, Journal of Educational Psychology, April, May and June, 1914, and September, October, November, and December, 1917. Other references are contained in the Bibliography by L. W. Crafts ([9]).