The core of demographic studies has 3 component concerns:
- Births
- Deaths
- Migration
All of demography can be reduced to this very simple formula:
(Births-Deaths) +/- [(In-Migration)-(Out Migration)] =
Population Change
You are likely familiar with "birth" and "death," but might not be as familiar with the term "migration."
Migration is the act of going from one region, country, or place to another.
Now that you know what migration means, examine the formula again:
(Births-Deaths) +/- [(In-Migration)-(Out Migration)] =
Population Change
The first part of the formula, births minus deaths, is called natural increase. It means all births minus all deaths in a given population over a given time period.
The second part of the formula is called net migration is the in-migration minus the out-migration in a given population over a given time period.
After determining the population change, you can also determine a population estimate. The final step to determining a population estimate is to take the population change and add it to the previous year's population. Most official population counts really are estimates. There are mistakes in counting that render results that are close, but never perfectly accurate.
Census enumeration is the formal counting of a population by its government.
The United States, along with many other countries, collects population data on a regular basis. You have already had the chance to examine a lot of population data throughout this course. The majority of that data has come from the U.S. Census Bureau and the Population Reference Bureau.
Consider the population change formula by looking at the U.S. population in 1990. Based on the U.S. Census, the U.S. population was 248,709,000. If you start the estimate with the 1990 population, you can run the numbers through the formula and derive an end of year 1999 population estimate. You can see the results of adding all the U.S. birth, death, and migration data for 1990-1999 in the table below:
| Births | -Deaths | +Net Migration | = Population Change |
|---|---|---|---|
| 39,860,00 | 22,711,000 | 9,580,000 | + 26,729,000 |
By the end of 1999, the population was estimated to be (1990) + (1990-1999 population change) = 1999 population or (248,709,000) + (26,729,000) = 275,438,000.
These estimates are very close to the actual July 1st, 1999 U.S. Census estimates.
The table to the right lists the 10 most populated countries of the world according to their populations in 2008. The U.S. ranks 3rd. The U.S. is one of the most populated nations of the world.
| Rank | Country | Estimated Population |
|---|---|---|
| 1 | China | 1,324,700,000 |
| 2 | India | 1,149,300,000 |
| 3 | United States | 304,500,000 |
| 4 | Indonesia | 239,900,000 |
| 5 | Brazil | 195,100,000 |
| 6 | Pakistan | 172,800,00 |
| 7 | Nigeria | 148,100,000 |
| 8 | Bangladesh | 147,300,000 |
| 9 | Russia | 141,900,000 |
| 10 | Japan | 127,700,000 |
This table shows the population estimate for the 2050. The United States is still number 3 on the list, but interestingly, it is projected that India will rank 1st and China 2nd.
| Rank | Country | Estimated Population |
|---|---|---|
| 1 | India | 1,755,200,000 |
| 2 | China | 1,437,000,000 |
| 3 | United States | 438,200,000 |
| 4 | Indonesia | 343,100,000 |
| 5 | Pakistan | 295,200,000 |
| 6 | Nigeria | 282,200,000 |
| 7 | Brazil | 259,800,000 |
| 8 | Bangladesh | 215,100,000 |
| 9 | Congo, De. Rep. | 189,300,000 |
| 10 | Philippines | 150,100,000 |
