1 February 2009 Variation of the Probability of a Male Birth Within and between Sibships
William H. James
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Stansfield and Carlton [Human Biology 79:255–260 (2007)] reported that the distributions of the combinations of the sexes in human sibships are binomial. They inferred that the probabilities of male births are equal and independent within and across all sibships. Here I argue that their argument is both invalid and false. Contrary to their inference, a binomial distribution may result when equal and counterbalancing measures of Poisson and Lexis variation are simultaneously present. These conditions are approximately met with respect to human births.

Copyright © 2009 Wayne State University Press, Detroit, Michigan 48201–1309
William H. James "Variation of the Probability of a Male Birth Within and between Sibships," Human Biology 81(1), 13-22, (1 February 2009). https://doi.org/10.3378/027.081.0102
Received: 11 January 2008; Accepted: 1 January 2009; Published: 1 February 2009
binomial distribution
Poisson variation
sex ratio
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