to get a better idea of a demographics is to simply look at population pyramids. birth rates aren't a good way to gauge whether a population will in the future increase or decrease due to complexities such as ageing population, mass migration of work forces, people having children late in life and/or over a longer period of time. similarly childless rates aren't good as a can have higher childlessness rate than b, but in a those having children are having more children.
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