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Category: Project

Description: Recent methodological advances in indirect migration and mortality estimation reveal important unforeseen patterns underlying these population processes, yet accurate indirect estimation of fertility remains difficult. The primary fertility index for a population, the total fertility rate (TFR), requires data on births disaggregated by mother’s age and thus cannot be calculated for the many areas and time periods that lack such information. Here we discuss a universal methodological framework for estimating TFR using inputs as minimal as the age-sex structure of a population. We show that the implied total fertility rate (iTFR) accurately estimates fertility from a population's age-sex structure in a wide range of scales, time periods, and even species. We also discuss two extensions of the iTFR that offer improved accuracy with minimal additional data requirements. To demonstrate the utility of this approach, we produce the first complete county-level map of U.S. fertility, reconstruct historical TFRs for 1000 additional country-years up to 150 years prior to the collection of birth records, and estimate TFR for the U.S. conditioned on household income, a variable unrecorded on U.S. birth records. Given its parameter-free nature, the method has wide applicability across space and time. We anticipate that our methodological framework will allow extension of fertility analysis to new sub-populations, time periods, and geographies, expanding our ability to understand fertility processes.