Demographic Balancing Equation, Natural Increase & Net Migration

Lesson Transcript
Instructor: Christopher Muscato

Chris has a master's degree in history and teaches at the University of Northern Colorado.

How do we figure out the population on a year-to-year basis? Explore the ideas behind the demographic balancing equation, natural increase, and net migration in this lesson. Then test your understanding with a brief quiz.


We need to figure out how many people are in our community. Why? Pick a reason! We've got potholes to fix, and we need to know how many taxpayers there are. We're going to have to pay for public schools, and we need to predict the number of children. We've got to stock health clinics, post offices, and government offices with enough people and supplies to meet the public's needs.

I mean, what if we run out of marriage licenses or bandages or stamps or cafeteria lunches? We'd have an uprising on our hands! So we need to know a lot of information about this community, and for that we turn to demographics, the statistical analysis of a population. And then we can get to work fixing all those problems.

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Coming up next: Thomas Malthus' Theory of Human Population Growth

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  • 0:01 Demographics
  • 0:48 Demographic Balancing Equation
  • 1:40 Natural Increase
  • 2:31 Net Migration
  • 3:10 Calculating the Equation
  • 4:45 Lesson Summary
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The Demographic Balancing Equation

Demographics can tell us a lot of information, but counting every single member of the population takes a lot of work. Really, the government only does this once every ten years with the national census, the most thorough demographical record of a nation. This counts as much as it can, but in between those ten years, it's still important to know how many people you're dealing with.

So rather than re-count every person every year, we simply turn to the demographic balancing equation which calculates population change from year to year. The equation itself is actually pretty simple: total population +/- natural increase +/- net migration = balanced population. See, simple - except that there are a few terms in here that we probably should define!

Natural Increase

One of the things we need to know in order to calculate the demographic balancing equation is natural increase, or the population change from births and deaths. Calculating this is pretty easy - just subtract the number of deaths from number of births; that's how much your population increased or decreased from natural causes.

We can get this information without having to ask every person if they've had any births or deaths in the family because these are vital statistics, those statistics that only need to be recorded once through legal documents like birth and death certificates. Those are already on record, so getting that information is a lot easier that conducting a census. So are we ready to calculate the demographic balancing equation? Well, hold your horses, 'cause there's still one more term to figure out.

Net Migration

As anyone living in the United States should realize, people enter this country in more ways than just birth and leave in other ways besides death. After all, what kind of melting pot would we be without all the world's peoples? Net migration counts the total number of immigrants who enter an area and emigrants who leave. So the formula is just immigrants minus emigrants, and there's your population change from unnatural causes. Not unnatural; immigration isn't unnatural, non-natural causes. There we go! And now, we are ready to calculate that equation.

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