| Abstract: | Birth squeezes result from an imbalance in the number of males and females in the childbearing ages, and can have a significant impact on the level and distribution of births. To measure the effects of a birth squeeze, the observed male and female age-specific birth rates were distinguished from the underlying fertility magnitudes, which reflect the mutual propensity of males and females of specified ages to have a child. The fertility magnitudes, readily expressible in terms of the birth rates, are nonetheless independent of the age-sex composition of the population, while the birth rates are affected by compositional changes. The two-sex Total Fertility Rate, TFR2, the average of the male and female TFRs, is advanced as a summary measure of fertility independent of the birth squeeze, and a simple index, U, is defined to measure the severity of the squeeze. Analyses involving stable population models, alternative population projections, and the birth squeezes found in contemporary populations documented the importance of the birth squeeze for studies of fertility. In particular, the size of the distortions introduced by the birth squeeze was seen as related to the level of fertility itself. In high-fertility populations, the birth squeeze depresses observed female age-specific birth rates, and thus conventional measures can significantly underestimate the fertility reduction needed to end population growth. |
