Female, male, two-sex fertility rates and their population projections

Fertility behavior is jointly determined by both the mother and the father. However, fertility is traditionally defined as the number of children born to women in demography and related studies. Consequently, the female total fertility rate (TFR) becomes the most important indicator of fertility level, and the population projections issued by the governments and the United Nations are female renewal, of which the births are produced by women only. The absence of men has historically been attributed to the lack of available male fertility data. However, with advancements in data collection and analysis, men's fertility rates can be calculated for most countries of the world, leading to increasingly available male TFRs and male-renewal population projections. This leads to the question of which TFR and population projection, female or male, female renewal or male renewal, should be used to indicate fertility level and to serve various socioeconomic programs. Using the data from the G7 countries around 2020, we show that the differences between female and male TFRs range from 0.6% in France to 8.4% in Italy. Assuming constant mortality and fertility rates and zero migration for the G7 countries, the median difference between the annual births in female-renewal and male-renewal population projections reaches 9% in 2100. To address these inconsistencies, we propose that two-sex fertility rates and two-sex renewal population projections could be a solution.