Colloquium in January 2026
Bongoh Kye(Kookmin University)
This study presents findings on the relationship between household income and fertility using administrative data. Although the relationship between income and fertility is of great importance in fertility research, data limitations have made it difficult to produce reliable findings on this topic. To overcome these limitations, this study analyzes the relationship between equivalized household income quintiles and fertility using two large-scale administrative datasets: the National Health Insurance Database and the Statistical Register.
The findings from these two datasets can be summarized as follows. First, a declining trend in fertility rates was observed across all household income quintile groups from 2015 to 2023. Second, while the analysis using the National Health Insurance Database reveals a U-shaped relationship between household income and fertility, the analysis using the Statistical Register shows an inverse U-shaped relationship between the two. This study discusses the reasons for these contrasting patterns. Third, the decomposition analysis of changes in fertility rates and the number of births by age and household income decile—examining changes in the proportion of married women, marital fertility rates, and the number of women—demonstrates that the decline in the total fertility rate and the number of births between 2015 and 2023 was primarily driven by the decrease in marital fertility rates across age groups and household income quintiles. Finally, this study discusses the implications of the findings as well as the possibilities and limitations of fertility research using administrative data.
