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April 1934


Arch NeurPsych. 1934;31(4):824-836. doi:10.1001/archneurpsyc.1934.02250040148011

Ratios ranging from 1 in 80 to 1 in 90 are given for the occurrence of twin births in the new-born population. In the United States1 for the years from 1920 to 1929, inclusive, the ratio was 1 in 87 and in Minnesota1 1 in 78. Muller,2 Orel3 and von Verschuer4 devised formulas for calculating the probability that given twins are identical when data can be obtained concerning certain unrelated physical characters of the twins and their siblings. Weinberg5 and Knibbs6 have differential methods for calculating the number of identical human twins. Table 1

is constructed from the statistics of the United States Bureau of Census 1 for the years 1920 to 1929, inclusive. The figures include white and colored twins, both twins living, one twin living and both twins stillborn.

Monozygotism is commonly predicated on the same chorion, a single placenta and