Estimating the intrinsic rate of increase of a population from the average numbers of younger and older sisters

Based on stable population theory, a mathematical relationship is developed between the intrinsic rate of increase (r) of a population and the ratio (Z) of the average number of younger sisters ever born to the average number of older sisters ever born, for a random sample of women in the population. This mathematical formula is then converted into a technique for estimating r from data on numbers of sisters. The extent to which the technique may be generalizable to actual populations is discussed.