Background: The total fertility rate (TFR) in South Korea has fallen below 1.3 since 2001. The role of the rapid shift toward a late-childbearing pattern in driving Korean fertility decline to this ultra-low level has been little explored until now. Objective: We provide an in-depth analysis of period fertility trends by birth order in South Korea from 1981 to 2015, when the period TFR fell from 2.57 to extremely low levels. Methods: We combine census and birth registration data to estimate period and cohort fertility indicators by birth order. We compare changes in conventional TFR with tempo- and parity-adjusted total fertility rate (TFRp*) and their birth-order-specific components. Results: The tempo effect linked to the shift toward delayed childbearing has had a strong and persistent negative influence on period TFRs in South Korea since the early 1980s. Without the shift to later childbearing, period fertility rates in South Korea would consistently stay higher and decline more gradually, reaching a threshold of very low fertility, 1.5, only in 2014. The postponement of childbearing and the resulting tempo effect were strongest in the early 2000s, when Korean TFR reached the lowest levels. More recently, Korean fertility has been characterized by a diminishing tempo effect and falling first and second birth rates. This trend marks a break with the previous pattern of almost universal fertility and a strong two-child family model. Contribution: Our study demonstrates the importance of the tempo effect in explaining the shift to ultra-low fertility in South Korea and in East Asia.

臺灣在二十世紀中完成了人口轉型，特別是生育轉型的幅度與速度最為劇烈。也正因為生育轉型過於成功，臺灣此刻正面臨超低生育率導致的人口衰滅危機。近年來，人口學界針對生育率變遷，熱中於探討生育率的步調（tempo）與數量（quantum）效應，藉此瞭解時期生育率變遷的趨勢。 生育步調與數量的分析，本質上仍是時期性測量，未能真正瞭解年輪生育率的變遷，以致對於時期生育率趨勢的分析無法解決根本問題。這個現象，對於臺灣生育率研究特別必須加以處理。然而，臺灣雖然是人口資料的「寶庫」，有關生育的人口統計，卻只有存在於二十世紀下半葉，亦即，二十世紀前半葉的完整生育統計已經無法獲取。本研究試圖結合人口普查、戶籍統計，以及抽樣調查資料，運用參數式模型（parametric mode）和人口轉換（demographic translation）等人口分析方法，嘗試重建二十世紀完整的時期與年輪生育率，藉此，分析年輪生育率與時期生育率之間的變遷關係，最終瞭解未來生育率發展的可能後果。 / Demographic Transition has been completed during the middle of 20th century in Taiwan, and the extent and speed of transition are spectacularly rapid. Due to the over succeed of the demographic transition, lowest-low fertility pattern has stricken Taiwan society and probably led to a horrible extinction. Recently, in order to project the pattern of fertility rate, demographers endeavored to figure out how tempo and quantum effects contribute to fertility rate. Unfortunately, analysis of tempo and quantum effects is essentially periodic measurement. It leads no way to understand the pattern of cohort fertility in Taiwan. However, although Taiwan’s demographic statistics is well known as the world’s treasure trove, the fertility statistics are available for only 50 years. It means that we are not capable of having the first half 20th century’s fertility rate in Taiwan. We use demographic analytic methods such as parametric mode and demographic translation to analyze combined data which is constituted of census data, vital statistics, and survey data. The object of this research is to re-build the 20th century’s fertility rate in Taiwan. Once we have the intact fertility rate in 20th century, we could realize the pattern of period and cohort fertility transition. Furthermore, we will have a better chance to project Taiwan’s fertility rate in the future.