Note 36 — Chapter IV
Reading edition
Thorndike, E. L., "Measurements of Twins," Arch. of Philos., Psych. and Sci. Methods, No. 1, New York, 1905; summarized in his Educational Psychology, Vol. III, pp. 247-251, New York, 1914. Measured on a scale where 1 = identity, he found that twins showed a resemblance to each other of about .75, while ordinary brothers of about the same age resembled each other to the extent of about .50 only. The resemblance was approximately the same in both physical and mental traits.