Has U.S. Fertility Declined? The Answer Depends on Use of a Period Versus Cohort Measure of Fertility

Lawrence L. Wu , New York University (NYU)
Nicholas Mark, New York University

In this paper, we show that period and cohort fertility measures yield strikingly different pictures of trends in U.S. fertility. Trends using the total fertility rate (TFR) and data from vital birth registers, the standard measure reported in widely publicized NCHS publications, suggest sharp declines in U.S. fertility, from an above-replacement level of 2.48 in 1970 to a below-replacement level of 1.76 in 2017. Using the same birth register data, we show that the cumulative number of births for successive birth cohorts of U.S. women suggest far more modest trends, with cohorts that have completed their fertility at or above replacement levels. We conclude that both TFR and cohort measures should be used to describe U.S. fertility trends, with our findings also reemphasizing well-known quantum and tempo distortions that can bias TFR-based analyses.

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 Presented in Session 210. Flash Session: Recent Trends in Fertility and Contraception in the United States