Niger also boasts the world's highest birth rate, with 44.2 births per 1,000 inhabitants. The Democratic Republic of the Congo, Mali, and Chad are next with 5.9, 5.9, and 5.7 children per woman, respectively. Iraq has the lowest birth rate, at 3.3 babies per woman. The most reliable data source for fertility rates is the World Health Organization (WHO). It collects information on all countries' reproductive health practices through a series of surveys called Demographic and Health Surveys (DHS). The most recent edition was conducted in Nigeria from 2006 to 2010. After analyzing responses from women aged 15-49, WHO reports that the total fertility rate in Niger is 6.3 children per woman. This means that after multiplying 6.3 by 1000 to get an estimate of the number of births needed to replace the population, you get 57,300 births needed every 10 years just to keep populations stable. Although DHS does not ask about cause of death, the leading causes of death for children under five years old are similar to those for older children and adults. These include respiratory infections, diarrhea, malaria, malnutrition, and childbirth complications. In addition to the DHS, the United Nations Population Division compiles estimates on fertility rates based on data collected from a variety of sources including governments, international organizations, and private companies.