Hitherto two methods have been commonly used to measure dementia—by means of numerical measures of scatter, and by means of the discrepancy between scores on vocabulary and other tests. In the present investigation the value of the most popular techniques with both methods was examined, and a new short measure of dementia was evolved.

Subjects taking the Stanford Binet and similar tests rarely pass abruptly from complete success at and below a certain M.A. level to complete failure at the next and subsequent levels. For example, a subject with a total M.A. of eleven years may succeed in all the subtests at and below the VIII year level and fail all the subtests above the XIV year level, while between these two levels he succeeds in some and fails others. The range of partial success and failure is called the “scatter.” Many psychometrists believe that unusually wide scatter indicates psychopathy or intellectual deterioration. The various methods for measuring scatter are conveniently summarized by Harris and Shakow (1937).

A long-standing observation on the results of intelligence tests in dementia is that vocabulary ability remains comparatively unimpaired until a late stage when the subject is unable to solve other tests. Therefore, it has been claimed, vocabulary score may be taken as a measure of the subject's pre-morbid intelligence, and the discrepancy between his vocabulary ability and ability on other tests as a reflection of the difference between his former and present intelligence, thus providing a measure of his dementia. The Babcock test is the best known of several techniques, based on this principle, for the measurement of dementia.