Measurement in Mental Deficiency

The study of mental deficiency can be said to be based upon measurement. It is biometrical in a way that the rest of psychiatry is not, because the ultimate criteria for diagnosis of mental defect (or subnormality) are quantitative. Some kind of intelligence measurement or rating is always implied, and even at the lowest level quite often a measurement is actually made. In this lecture I shall only be able to outline my subject by giving examples.