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Relating Period and Cohort Fertility
1Population Research Institute, Pennsylvania State University, University Park, PA, USA.
Demography
|April 25, 2022
Summary
This study reveals a simple link between period and cohort fertility, showing period total fertility approximates the fertility of the previous generation
Area of Science:
- Demography
- Population Studies
- Fertility Analysis
Background:
- Total fertility rates (TFR) are influenced by both time periods and birth cohorts.
- Understanding the relationship between period and cohort fertility is crucial for population dynamics.
Purpose of the Study:
- To derive explicit relationships between period and cohort fertility.
- To establish a link between period/cohort fertility and the average fertility of childbearing cohorts (ACF).
Main Methods:
- Utilized age-specific fertility rates to model period and cohort fertility.
- Assumed constant age-specific fertility proportions to derive new relationships.
- Compared derived cohort fertility values with observed U.S. data (1917-2019) using a cubic curve assumption.
Main Results:
- Period total fertility is approximately equal to the total fertility of the preceding generation's cohort, with a minor adjustment.
- A straightforward relationship connects period and cohort fertility to ACF.
- Despite assumption violations, derived U.S. cohort fertility values showed only a 7-8% average deviation from observed data.
Conclusions:
- The derived relationships offer a simplified yet accurate method for linking period and cohort fertility.
- Short-term projections indicate a continued decline in U.S. cohort fertility.
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