To estimate the number of women pregnant at any time in China, they have
Firstly, they have solved for the % of women pregnant any time and arrived at (2%)
Secondly, they have assumed that 50% of China's population as women.
Thirdly, they have directly multiplied 2% with the total women count in China.
Shouldn't we segment the women population again into age-groups before the aforementioned 3rd step to get a realistic number of pregnant women in China?
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Agree. The easiest approach would be to use the replacement effect in determining the birth rate. If we consider the population is 1.4B and average life expectancy as 70 years, we would get the birth rate as 20M and that equals the number of pregnant women in China at any given time, assuming that the population growth is negligible.
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