Birth rate
The region of Sub-Saharan Africa has the highest birth rate in the world. As of 2016, Niger, Mali, Uganda, Zambia, and Burundi have the highest birth rates in the world. This is part of the fertility-income paradox, as these countries are very poor, and it may seem counter-intuitive for families there to have so many children. The inverse relationship between income and fertility has been termed a "demographic-economic "paradox"" by the notion that greater means would enable the production of more offspring as suggested by the influential Thomas Malthus.
Irish Free State
According to one report, in 1924, shortly after the Irish Free State's establishment, the new dominion had the "lowest birth-rate in the world". The report noted that amongst countries for which statistics were available (Ceylon, Chile, Japan, Spain, South Africa, Netherlands, Canada, Germany, Australia, United States, Britain, New Zealand, Finland and the Irish Free State). Ceylon had the highest birth rate at 40.8 per 1,000 while the Irish Free State had a birth rate of just 18.6 per 1,000.