The Likelihood of Persistently Low Global Fertility
评估低生育率是否可能成为全球持续现象，区分队列生育率与时期生育率，发现队列生育率下降后未反弹，且终身无孩率上升和家庭规模缩小是主因，结论是长期看低生育率很可能持续。
For the world as a whole, average birth rates have been falling for decades—from about 5 in 1950 to a little above 2 today. Two-thirds of people today live in a country where the birth rate is below an average of two children per two adults, which means below the fertility level needed to sustain population sizes (without net migration). In this paper, we assess whether low fertility is likely to persist as a global phenomenon. We distinguish cohort birth rates, which matter for generation-to-generation population change, from period birth rates, which present a snapshot of birth rates at a point in time, but may offer less insight on longer-run possibilities. Where cohort birth rates have fallen low, they have not subsequently rebounded. We show that both increasing rates of lifetime childlessness and smaller family sizes among parents have contributed to falling cohort birth rates. Pronatal policies, we discuss, can have large effects on the annual fertility data without substantially changing the average number of children women have over their lifetimes. Although future birth rates remain uncertain, we conclude from the evidence that, over a long horizon, persistent low fertility is a likely future.