The probability that a pregnancy will yield a boy given previous children sex ratio

Range 51.45 + 0.3n - 0.5m %
Organism Human Homo sapiens
Reference James WH. Sex ratio and the sex composition of the existing sibs. Ann Hum Genet. 1975 Jan38(3):371-8.PubMed ID1137352
Primary Source Malinvaud, E. (1955). Relations entre la composition des familles et le taux de masculinite. Journal de la societe de Statistique de Paris, 96, 49.
Method Based on a study of 4 million births in France between 1946-1950
Comments n is number of pre-existing boys and m is the number of pre-existing girls. Notice that ratio in population depends on viability rates that actually shifts ratio towards females.
Entered by Ron Milo - Admin
ID 101075