Measures of marriage based on the data for one sex only do not give a fair comparison between two communities unless the relative numbers and ages of the sexes available for marriage are the same in both. Such a similarity is unlikely to exist; in 1921, for example, at ages 15–54 the number of marriageable women was 87% of the number of marriageable men in New Zealand but the corresponding ratio in England and Wales was 119%, and this fell to 113% by 1931.

W. S. Hocking discussed the balance of the sexes in Great Britain in J.I.A. (74, 340) and showed the extent of variations in the relative numbers available for marriage in England and Wales in this Journal (10, 24). It is desirable in a number of problems to be able to make some allowance for such variations, particularly in connexion with the measurement of reproduction, depending as it does on marriage intensity.