THE DEVELOPMENT OF MENTAL TESTS
IT seems clear that the eventual significance of the "types" that we considered in the last chapter and of the many others that have been proposed must depend upon their treatment by statistical methods. Such statistical methods are now available, having entered psychology by another channel, that of mental tests. We have seen how both the mental test and the corresponding statistical procedures originated with Galton and were developed by Cattell. We have called attention also to two important adumbrations of mental testing, as it was later to be practised, the "combination method" of Ebbinghaus and in the various experiments which Binet carried out on his daughters.
As in so many other cases, the stimulus to further progress in this field came largely from problems connected with the abnormal. In 1904, the year after the appearance of his Étude Expérimentale, Binet was asked by the French Minister of Public Instruction to serve on a committee appointed to study methods of dealing with the "backward" child. One of the most important problems encountered by this committee was to find some means of distinguishing between lack of ability on the one hand, and laziness or lack of interest on the other. Together with Simon, Binet devised a series of tests arranged in order of increasing difficulty. First published in 1905, these tests underwent a number of revisions, reappearing with modifications and additions in 1908 and again in 1911. In their later form the tests aimed at measuring intelligence in terms of "mental age", i.e. at establishing norms for each year of growth, and with their