The Natural Increase Rate and the Demographic Accounting Equation are both calculations used to determine the current or projected population growth of a region. The Demographic Accounting Equation is more comprehensive because it takes into account immigration and emigration, whereas the Natural Increase Rate only takes into account the birth and death rates.

An Essay on the Principle of Population, published at the end of the eighteenth century, was written by Thomas Malthus. In this essay, Malthus argues that the rate of food production grows arithmetically, whereas population grows exponentially. Malthus argued that this would lead to a situation where population outstrips food production, leading to widespread famine and starvation. His writings are extremely influential even to this day; however, many geographers dispute his conclusions and argue that technology augments food production, allowing it to keep up with population growth. It remains to be seen whether Malthus’ predictions will come true in the twenty-first century or beyond.

The Demographic Transition Model can be divided into pre-industrial, transitional, and industrial segments. A pre-industrial country (like Somalia, for example) will have high birth rates and high death rates. This is the starting place for all of humanity—many people being born and many people quickly dying. The next phase is transitional; in this phase, first the death rate starts dropping, and then shortly thereafter, the birth rate begins to drop too. The final phase is called "industrial." When a country is well-developed and women are relatively liberated, then birth rates and death rates remain fairly stable and much, much lower than in a pre-industrial society.

The stationary population level (SPL) is the level at which a population cannot grow any more.

The stationary population level (SPL) is the level at which a population cannot grow any more.

Demography is the study of human population. Specifically, demography generally involves the study of statistics concerning things like birth and death rates, fertility and public health, income, ethnicity, and outbreaks of disease.

The crude death rate or CDR is the ratio of the number of deaths yearly per 1,000 people in a given population.

In highly developed countries like the United States the natural increase rate is generally very low, it might even be negative. But, the natural increase rate only reflects the changes in population caused by births and deaths; it does not consider immigration and emigration. Much of the population growth in the United States is driven by immigration and the fact that newly arrived immigrants are much more likely to have large families.

The natural increase rate does not consider immigration or emigration. It is determined by subtracting the number of deaths from the number of births in a given region. So, if there are ten thousand deaths and thirteen thousand births in a given region, in a given time period, the natural increase rate is three thousand.

The Demographic Transition Model can be divided into pre-industrial, transitional, and industrial segments. A pre-industrial country (like Somalia, for example) will have high birth rates and high death rates. This is the starting place for all of humanity—many people being born and many people quickly dying. The next phase is transitional; in this phase, first the death rate starts dropping, and then shortly thereafter, the birth rate begins to drop too. The final phase is called "industrial." When a country is well-developed and women are relatively liberated, then birth rates and death rates remain fairly stable and much, much lower than in a pre-industrial society.