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.

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 accounting equation” is used to predict future population growth for a region or country. It is determined first by calculating the “natural increase rate,” which is the number of births minus the number of deaths. Then by adding the “natural increase rate” to the “net migration number.” The “net migration number” is the number of immigrants minus the number of emigrants in a given time period.

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.

In stage three of the demographic transition model a country’s death rate has already fallen and it’s birth rate is in the process of falling as well. The death rate in Morocco has fallen dramatically in the half-century since independence, but the birth rate has only recently begun to fall to match this decline. Nigeria and South Sudan are both still in stage two of the demographic transition process (falling death rates, steady birth rates); Sweden and Denmark are both in stage four of the demographic transition process (low death rates, low birth rates).

All of these countries are in either stage two or stage three (the transitional stages) of the demographic transition model, except Japan, which is in stage four. Stage four is generally considered the final stage of the demographic transition model. In stage four, the birth rates and the death rates are both low and generally steady. In Japan, the death rate is very low and the birth rate is very low, leading to a steady population and perhaps even a slight population decline.

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 “doubling time” refers to the amount of time it takes for the population of a region to double. The number is based on the annual increase in population as a percentage of the original population. An annual increase of one percent of the population will cause the population to have a “doubling time” of seventy years. An annual increase of four percent of the population will lead to a “doubling time” of sixteen years. This might seem incredibly fast, and indeed it is. The reason for this is that population compounds as it grows, much like compound interest.

All of these answer choices affect the “natural increase rate” of a country. The following are general rules, of which there are some exceptions: as access to education becomes more universal the “natural increase rate” will decline; government policies that institute population control programs will cause the “natural increase rate” to decline; the more empowered women are in a society, and the more gender equality there is, the lower the “natural increase rate.” Finally, cultural customs—like emphasizing the importance of motherhood—can have significant impacts on the “natural increase rate.”

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.