title: The variation of the probability of a son within and across couples.
abstract: It is suggested that there is a flaw in the currently accepted account of the variation of P, the probability of a boy, within and across couples. It was previously suggested that P has a mean (for Caucasian couples) of approximately 0.514 with an SD of approximately 0.05 across couples: and that the variation within couples is rather less. Grounds are offered here for suspecting that this formulation underestimates both SDs by a factor of as much as 4. It is suggested that in estimating these sources of variation, earlier workers did not consider the possibility that within-couple variation might be random and substantial. In view of the established epidemiology of human sex ratios, it now seems likely that such variation exists, and that there is a substantial measure of counterbalancing across-couple variation.
authors.affiliation: The Galton Laboratory, University College London, Wolfson House, 4 Stephenson Way, London NW1 2HE, UK.
authors.forename: W H
authors.initials: WH
authors.lastname: James
mesh_terms: D005260:Female; D006801:Humans; D008297:Male; D008390:Markov Chains; D015233:Models, Statistical; D016012:Poisson Distribution; D011247:Pregnancy; D011336:Probability; D012744:Sex Ratio