This excellent monograph reports the findings, summary and conclusions of a study of 366 pairs of twins with mental deficiency in one or both of each pair. The chief purpose of the observation was to gather information on the etiology of mental deficiency.
The authors attempted to determine whether the factors producing mental deficiency were pregerminal, germinal, embryonic, intranatal or postnatal. The material was gathered from many institutions and cities. The intelligence quotient of the patients was the measure of intelligence used. A brief summary of data on each pair of twins is included in the report. These case histories and reported findings, however, are not sufficiently complete to allow the reader to arrive at definite conclusions.
Some of the conclusions reached are:
Mental deficiency and some of its complicating conditions are more common in the male.
The sex distribution of intelligence is unequal, the female sex being