The Age of Migration的意思|示意

And although migration is the only thing which prevents many European populations from shrinking, an influx of outsiders will not change age-structures by much.

虽然吸取移民是唯一的可以阻止欧洲人口缩减的方法，但是流入的外来移民不会对年龄结构产生很大的改变。

The average quantities, average rate of age spcific migration and average age specific population in the four years from 1985 to 1989 can be estimated by using this method.

据此方法可得出1985年到1989年四年间平均按龄迁移量、平均按龄人口数及平均按龄迁移率。