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.
Infant mortality
Collecting the accurate statistics of infant mortality rate could be an issue in some rural communities in developing countries. In those communities, some other alternative methods for calculating infant mortality rate are emerged, for example, popular death reporting and household survey.
The country-to-country variation in child mortality rates is huge, and growing wider despite the progress. Among the world's roughly 200 nations, only Somalia showed no decrease in the under-5 mortality rate over the past two decades.The lowest rate in 2011 was in Singapore, which had 2.6 deaths of children under age 5 per 1,000 live births. The highest was in Sierra Leone, which had 185 child deaths per 1,000 births. The global rate is 51 deaths per 1,000 births. For the United States, the rate is eight per 1,000 births.