AN ANALYSIS OF GEISSLER'S DATA ON THE HUMAN SEX RATIO

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Abstract
Summary: Skellam's modified binomial distribution is described, and fitted to Geissler's data on the sex ratio in human families of from 2 to 12 children. It is concluded thatp, the probability of a birth being male, varies between families of the same size, having a variance of about 0–0025 amongst a complete cross‐section of a nineteenth‐century German population, and that there is no evidence for the existence of parents only capable of producing unisexual families. Assuming thatpvaries within a family, the apparent anomalies would appear to be explicable. The critical conclusions of Lancaster regarding the reliability of Geissler's data are briefly examined. In an appendix, the derivation of the posterior probability distribution ofpfor a couple with a known number of boys and girls is given.