Dynamic Demographic Analysis pp 9-29 | Cite as

# Amplified Changes: An Analysis of Four Dynamic Fertility Models

## Abstract

Fertility change over time can be modeled in a variety of ways. Implicit in each model is a story of the behavior driving fertility, and the assumptions behind each model provide insights into the forces that influence fertility. We present Ryder’s classic formulation of the translation between period and cohort measures of fertility, Lee’s moving-target model connecting fertility goals with period rates, the period-shift model of Bongaarts and Feeney, and the Goldstein and Cassidy cohort-shift model. All of these models have in common a simplified view of how fertility change occurs. An important lesson of all these formulations is that small variations in timing or targets can produce large fluctuations in period fertility, telling us that period fertility is particularly sensitive to changes in underlying aspects of the fertility process.

## Keywords

Total fertility rate Cohort fertility Fertility timing Fertility intentions Model comparison## References

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