ABSTRACT
Modern methods of psychological measurement, together with a growing interest in the qualitative aspects of the population problem both in England and in the U.S.A., have evoked numerous studies of the relative ability of different social groups within a community. The essential procedure adopted in these studies has been to compare average (mean) indices of ability, e.g. mean Intelligence Quotients. On this basis different social groups have been ranked in order of ability. Aside from the very dubious nature of the evidence adduced to support the general inference that any observed differences are exclusively or even predominantly genetic in origin, previous inquiries of this sort throw little light upon the fundamental problem to which this investigation is directed. However great may be the discrepancies recorded, the comparison of averages is of itself entirely inadequate to display the distribution of ability within a population of varied social composition.
