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This study of twins throws a beam of light on a portion of human knowledge which is badly in need of illumination, the influence of heredity in nervous and mental disorders. The authors have laboriously collected a mass of information concerning twins from institutional and other sources. They secured records for the surprising total of 1,014 pairs of twins one or both of whom had a mental disorder and 308 pairs of normal twins, serving as controls. The present study deals with 366 pairs of twins, one or both of whom were mentally deficient. The monograph includes brief case histories for each of the 366 pairs. Twenty-six tables epitomize the data from the case histories. Chief dependence is placed on measurements of intelligence (method not stated), an intelligence quotient below 85 being indicative of mental deficiency. To be counted as "both affected," twins must have intelligence quotients which do not
The Etiology of Mental Deficiency with Special Reference to Its Occurrence in Twins. Psychological Monographs, vol. 48, no. 4. Arch NeurPsych. 1938;40(1):221–222. doi:10.1001/archneurpsyc.1938.02270070231019
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