Cohort Effects or Period Effects?: Fertility Decline in South Korea in the 20th Century

Bongoh Kye, University of California, Los Angeles

This paper examines recent trends in fertility decline in South Korea. I attempt to answer two long-standing demographic questions using a unique Korean experience: 1) is fertility change driven by long-term cohort change or fluctuating period change? and 2) how is the level of completed fertility related to the timing of fertility? By using a classic age-period-cohort model, a moment decomposition method and a new summary fertility measure, ‘cross-sectional average fertility (CAF)’, I show that fertility change is primarily driven by period change and that delayed childbearing has important consequences for the onset of fertility decline. These findings are consistent with sociological accounts of fertility changes in Western countries: 1) temporal variations that cut across cohorts (e.g., economic cycles) are more important than shared socializing experiences within cohorts and 2) the onset of the fertility transition is driven by delays in childbearing.