Countries that do not have a well-functioning civil registration system only have approximate ideas of the Numbers, the longevity and the health of their population.

那些没有建立完善民事登记系统的国家对其人口的数量、寿命和健康状况，往往只有一些粗略的概念。

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A simple (though approximate) model of population growth is the Malthusian growth model.

一个简单的(虽然近似)模型的人口增长率是马尔萨斯的增长模式。

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We know that we are getting even older, and that the nearer a society approximate to zero population growth, the older its population is likely to be - at least, for any future that concerns us now.

我们知道我们越来越老，我们也知道一个社会的人口愈接近零增长，它的人口愈可能老龄化，至少就与我们直接相关的未来来说是这样的。

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For example, they only used the scores of players between the ages of 17 and 25 as a way to approximate the current undergraduate population.

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More specifically, imagine the simplest case of a population of a constant size - say a million (the approximate size of the Holy Land at the time of Jesus).

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