Sub-replacement fertility

Sub-replacement fertility is a total fertility rate (TFR) that (if sustained) leads to each new generation being less populous than the older is any rate below approximately 2.1 children born per woman, but the threshold can be as high as 3.4 in some developing countries because of higher mortality rates. Taken globally, the total fertility rate at replacement was 2.33 children per woman in 2003. This can be 'translated' as 2 children per woman to replace the parents, plus a 'third of a child' to make up for the higher probability of boys born and mortality prior to the end of a person's fertile life. Replacement level fertility in terms of the net reproduction rate (NRR) is exactly one, because the NRR takes both mortality rates and sex ratios at birth into account. As of 2010, about 48% (3.3 billion people) of the world population lives in nations with sub-replacement fertility. Nonetheless most of these countries still have growing populations due to immigration, population momentum and increase of the life expectancy. This includes most nations of Europe, Canada, Australia, Brazil, Russia, Iran, Tunisia, China, the United States and many others. In 2016, all European Union countries had a sub-replacement fertility rate, ranging from a low of 1.3 in Portugal, Poland, Greece, Spain and Cyprus to a high of 2.0 in France. The countries or areas that have the lowest fertility are in developed parts of East and Southeast Asia: Singapore, Hong Kong and South Korea. Only a few countries have had, for the time being, sufficiently sustained sub-replacement fertility (sometimes combined with other population factors like higher emigration than immigration) to have population decline, such as Japan, Germany, Lithuania, and Ukraine. As of 2016, the total fertility rate varied from 1.2 in Singapore, Hong Kong and South Korea to 7.2 in Niger. There have been a number of explanations for the general decline in fertility rates in much of the world, and the true explanation is almost certainly a combination of different factors. The fact that more people are going to colleges and universities, and are working to obtain more post-graduate degrees there, along with the soaring costs of education, have contributed greatly to postponing marriage in many cases, and bearing children at all, or fewer numbers of children. And the fact that the number of women getting higher education has increased has contributed to fewer of them getting married younger, if at all. In the US, for example, females make up more than half of all college students, which is a reversal from a few decades back. The relationship between higher education and childbearing varies by country: for example, in Switzerland by age 40, childlessness among women who had completed tertiary education is 40%, while in France it is only 15%. In some countries, childlessness has a longer tradition, and was common even before educational levels increased, but in others, such as Southern European ones, it is a recent phenomenon; for instance in Spain the childlessness rate for women aged 40–44 in 2011 was 21.60%, but historically throughout the 20th century it was around 10%. Not all countries show a relationship between low fertility and education: in Czech Republic, of women born in 1961-1965, low educated women were more likely to be childless than high educated women. The growth of wealth and human development are related to sub-replacement fertility, although a sudden drop in living conditions, such as the great depression, can also lower fertility. In Eastern European countries, the fall of communism was followed by an economic collapse in many of these countries in the 1990s. Some countries, such as those that experienced violent conflicts in the 1990s, were badly affected. Large numbers of people lost their jobs, and massive unemployment, lack of jobs outside the big cities, and economic uncertainty discourages people from having children. For instance, in Bosnia-Herzegovina, the total fertility rate in 2016 was only 1.28 children born/woman.