On Factors Affecting Fertility at Different Stages in the Reproduction History: An Exercise in Cohort Analysis

Abstract

Age-parity-specific birth probabilities and central birth rates cumulated over successive five-year age groups for U.S. birth cohorts (whites only) are analyzed using age, period, and cohort as possible independent variables. The main effects of age and period jointly account for virtually all of the variance of age-parity-specific birth probabilities; period accounts for a greater proportion of the variance at higher parities, while the opposite is true of age. The main effects of age and period and the age-period interaction jointly account for virtually all of the variation in central birth rates; about two-thirds of the overall age-period interaction is captured by the interaction components of observations in the age group 20 to 24 years. Both the variation by parity of the age and period effects on birth probabilities and the presence of age-period interaction in the case of reproduction in successive age segments, support the proposition that different fertility determinants come into prominence at different stages in reproduction history.