title: Cycle day of insemination, sex ratio of offspring and duration of gestation.
abstract: It has been reported that the regression of human sex ratio (number of males per 100 females at birth) on cycle day of insemination is U-shaped. The point is not yet established, so a search was made for possible effects of this phenomenon on the regression of sex ratio on duration of gestation (from last menstrual period to delivery). A previously unremarked feature of this latter regression is that it, too, is U-shaped. It is accordingly suggested that the one regression is responsible for the other, and a simple mathematical model indicates that the magnitudes of the two regressions are compatible with this conclusion.
authors.affiliation: Galton Laboratory, University College London.
authors.forename: W H
authors.initials: WH
authors.lastname: James
mesh_terms: D005260:Female; D006801:Humans; D007314:Insemination; D008297:Male; D011247:Pregnancy; D012744:Sex Ratio; D013997:Time Factors; D014481:United States