To assess the effects of the demographic transition, the two researchers split the sample into women born before 1870 and those born in or after it.
为了评估人口过渡的影响，这两名研究员分头对在1870年前和在这时及之后进行生产的妇女进行取样。
2
The number of individuals in different demographic groups who would have provided usable information if response rates were equivalent. See sample weighting.