Natural increase

In demographics, the rate of natural increase (RNI) is the crude birth rate minus the crude death rate. This rate excludes population increase from in migration and out migration. When looking at countries, it gives an idea of what position in the Demographic Transition Model, but to find out how much a country is growing, the population growth rate should be observed. The Demographic Transition Theory explains the rate of natural increase relate to the economic growth.

Usually developing countries have a positive or high natural increase rate. Developed countries have a negative/neutral or low natural increase rate, but many developed countries have their population increasing due to immigration despite their negative RNI. These countries also have the lower rate of death. This is because developing countries and developed countries are in different stages of the demographic transition. Developing countries are generally in the earlier stages of the transition meaning they have high fertility, which would show an increase in crude birth rates. Developed countries usually have lower or more stable fertility rates so they don't show as high rates in natural increase. This can be applied to mortality rates as well, because developing countries generally have higher mortality rates than developed countries. High mortality rates are due to differences in deaths from chronic and acute diseases.

The RNI can be shaped by government policy and a country's infrastructure. Policies can either encourage an increase in birth rates or discourage an increase in birth rates. For example China's one child policy was made to decrease birth rates therefore decreasing the RNI. A country with a good infrastructure to support families, women's health, and maternal/child health would likely have lower death rates from infant or maternal mortality.

The formula for the rate of natural increase is:

The result is the rate of natural increase in percentage form.

For example, Madagascar's crude birth rate (37.89) minus the crude death rate (7.97) is 29.92; divide that by 10 and the result is 2.992%, Madagascar's rate of natural increase.

The average global birth rate is 18.5 births per 1,000 total population in 2016. The death rate is 7.8 per 1,000 per year. The RNI is thus 1.07 percent.

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