We cannot say how much of the difference is the result of selectivity of migrants at the time of move and how much results from lowered fertility after moving to the urban setting.

我们无法说这个差距在多大程度上取决于移民时的选择，多大程度上取决于移民城市后生育力的下降。

youdao

And the difference was clear, with fertility declining by up to seven per cent with each extra year on a man's age between 41 and 45.

区别很明显，处于41岁到45岁之间的男人，每长一岁，生育能力下降的最大幅度为7%。

youdao

There was no significant difference in fertility rate, cleavage rate, high-quality embryonic rate and graftage embryonic number between these groups(P>0.05).

各组间受精率、卵裂率、优质胚胎率、移植胚胎数比较差异均无显著性（P>0.05）。

youdao

And in Iran, public policy and investment in family-planning services made the difference between rising fertility between 1979 and 1984 and falling fertility thereafter, not the rise in national incomes, nor female education.

ECONOMIST: Population booms, and busts