In the last number of the Journal of Hygiene we described an improved method of calculating birth-rates, by means of which exact correction can be made, in comparing the birth-rates of two communities or of the same community at different periods, for variations in the proportion of married women at childbearing ages, and for the different fertility-rates at different ages of childbearing life. The value of this method consists in the fact that by its means true differences in childbearing can be discovered, the differences due to variations of age or marital condition being eliminated.