The RATE of NATURAL INCREASE and Population Dynamics [AP Human Geography Review—Unit 2 Topic 4]

Geographers study population trends considering fertility rates, mortality rates, and migration. Fertility rates indicate a population's ability to have children, helping governments plan for infrastructure, education, and healthcare. Two ways to measure fertility rates are crude birth rate (CBR) and total fertility rate (TFR).

Crude birth rate (CBR) is the number of live births per thousand people in a year. While simple, it's considered 'crude' because it includes the entire population. A more accurate measure is the total fertility rate (TFR), which is the average number of children a woman will have during her childbearing years (15-49). A TFR of 2.1 is replacement level fertility; values below this indicate a declining population, as seen in Europe (1.6 TFR), while sub-Saharan Africa has a high TFR of around 4.6.

Mortality rates indicate a population's rate of deaths. The crude death rate (CDR) is the number of deaths per thousand people. Unlike CBR, CDR is a more accurate measure of death as it applies universally. The global CDR has decreased from 13 per thousand in 1960 to 8 per thousand currently, indicating increased life expectancy due to better nutrition, medicine, and clean water. However, life expectancy varies significantly by national and regional wealth.

The infant mortality rate (IMR) measures the number of children who die before age one per 1,000 live births. IMR is a strong indicator of a country's access to healthcare. High IMRs, such as in sub-Saharan Africa, suggest limited access to life-saving medical interventions for infants and mothers.

The rate of natural increase (RNI) is calculated as the crude birth rate minus the crude death rate. A positive RNI indicates population growth, a stable RNI suggests a stable population, and a negative RNI means population decline. However, RNI does not account for migration. Doubling time is the period it takes for a population to double at its current growth rate, with Nigeria having a short doubling time of 27 years due to rapid growth, compared to 233 years for the United States.

Social and cultural factors, such as religion (e.g., Roman Catholics and Muslims' views on birth control) and traditional gender roles, can significantly influence fertility rates. Political factors include pro-natalist policies (encouraging births in declining populations) and anti-natalist policies (restricting births, like China's former one-child policy). Economic factors also play a role; birth rates often decline during economic downturns and increase during economic booms. Economic disparities between countries can also drive migration, impacting population dynamics.