title: Distinguishing the impact of postponement, spacing and stopping on birth intervals: evidence from a model with heterogeneous fecundity.
abstract: This paper investigates the impact on birth intervals of three distinct birth control strategies: stopping childbearing, spacing births and the postponement of further childbearing for reasons unrelated to women's family-building histories. A macro-simulation model of the family-building process is described that incorporates heterogeneity in fecundability. This model is used to demonstrate that the postponement of further childbearing has a distinctive impact on schedules of duration-specific fertility rates that differs from that of both family-size limitation and birth spacing. In particular, the simulation results, supplemented by an analytical exposition, show that reductions in fertility due to spacing are a function of interval duration and its log, while reductions due to postponement are a function of interval duration and its square. This provides a way to test statistically for the presence of, and distinguish between, differential postponement and spacing in regression analyses of birth history data.
authors.affiliation: Department of Population Health, London School of Hygiene & Tropical Medicine, London, UK.
authors.forename: Ian M
authors.initials: IM
authors.lastname: Timæus
authors.forename: Tom A
authors.initials: TA
authors.lastname: Moultrie
mesh_terms: D000367:Age Factors; D001721:Birth Intervals / Q000706:statistics & numerical data*; D003267:Contraception / Q000706:statistics & numerical data*; D005191:Family Characteristics; D005260:Female; D005298:Fertility; D006801:Humans; D015233:Models, Statistical; D010298:Parity; D011247:Pregnancy