A kin-based measure of r and an evaluation of its effectiveness.

A relation is shown between r and the ratio (S) of those living who are youngest in their sibsets to those who are oldest. This extends Goldman's work on the relation between r and the ratio (Z) of younger to older ever born sisters. Solved for r, these relations provide kin-based measures of r. Tested against microsimulated population data, the S-based measure, though working from fewer observations per population, performs as well or better than any Z-based measure. Since the data needed to compute S make considerably fewer demands on respondents' knowledge, the S-based measure appears preferable in actual application.