While other countries have experienced a gradual decline in CBR since the 1990s, South Korea has shown a rapid decline and now has one of the lowest rates in the world. To identify what drives the decline of CBR, we apply a decomposition developed by Das Gupta (1993) to Korean registry data (KOSIS) and decompose CBR from 1990 to 2015 into four demographic factors: (1) the proportion of women of reproductive age, (2) the age structure of women of reproductive age, (3) the proportion married among women at each age group, and (4) the marital birth rate at each age group. The results show that the proportion of married among women is the main contributor to the decrease in CBR; a decline in the marriage rate is largely responsible for the low birth rate. The proportion of women of reproductive age and age structure of women of reproductive age are other factors lowering the CBR. Meanwhile, the marital birth rate contributes to an increase in CBR. Although some of the increases produced by marital birth rates could be an artifact of timing changes, the impact reflects the patterns of postponing marriage, which leads to more rapid births after marriage. This study uncovers important demographic factors like decreasing proportion married, the shrinking population in reproductive ages, and ageing among Korean women that drive the decline of CBR.

自 20 世纪 90 年代以来，其他国家的 CBR 逐渐下降，但韩国却出现了迅速下降，目前是世界上比率最低的国家之一。为了确定导致 CBR 下降的原因，我们将 Das Gupta（1993）对韩国登记数据（KOSIS）进行了分解，并将 1990 年至 2015 年的 CBR 分解为四个人口因素：（1）育龄妇女的比例， （2）育龄妇女的年龄结构；（3）各年龄组妇女的已婚比例；（4）各年龄组的婚生率。结果表明，女性已婚比例是导致CBR下降的主要原因；结婚率下降是低出生率的主要原因。育龄妇女比例和育龄妇女年龄结构是降低CBR的其他因素。同时，婚内生育率也促进了CBR的增加。尽管婚内出生率的增加可能是时间变化造成的，但其影响反映了推迟结婚的模式，这导致婚后出生速度加快。这项研究揭示了导致 CBR 下降的重要人口因素，例如已婚比例下降、育龄人口减少以及韩国女性老龄化。