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Population Growth

Population Growth

Author: Paul Hannan

Identify the determinants of population growth.

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Source: Intro Music by Mark Hannan; Public Domain Images from; Public Domain

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[MUSIC PLAYING] Welcome to this episode of Sociology, Studies of Society. Today's lesson is on population growth. As always, don't be afraid to pause, stop, rewind, or even fast forward to make sure you get the most out of this tutorial. Today, we're looking at population growth. So when we're looking at population growth, there's really this equation that is used by people who look at populations to help understand a population.

So the equation is B minus D plus I minus E. Now that seems really confusing when we look at it here. But let me go through exactly what makes the different components up, and it'll make total sense by the end. So population equals births minus deaths plus immigration minus emigration. Pretty simple, but let's make sure we got it.

So things that make population go up. Well, in general, fertility is the ability for an individual or population to have children. And fertility then, of course, affects population. But specifically, when we're looking at that equation, there's two things that go into looking at an increase in your population. We have the birth rate, and we have immigration.

So birth rate are the number of births over a specific time. Normally, birth rate gets translated to births in a year for every thousand people. And that's the way that you can communicate that number pretty consistently. But technically, you could change the amount of time, and you could change the rates to be different ratios. It could be out of every 10. It could be out of every a million. It could be many different things. But you're looking at, basically, how many people are born every year.

Now immigration, on the other hand, is how many people move into an area. So migration is moving in or out. And immigration is people moving in, so that's going to increase your population. If you're a town of 10 and a new business moves in that has 30 people move into your community, well, now you're community has 40 people. There is an increase in your population.

Now there are also things that can decrease your population. And in general, most of these things fall under the idea of mortality. So mortality is looking at the opposite really of fertility, and that's how frequently death happens within a population. So we have death rate, life expectancy, infant mortality rate, and emigration.

So death rate is the rate of deaths over a specific time. That's similar to birth rate. So, generally, it's out of every thousand, and we're looking at it over a year. But it could vary. So how many people die over a specific time? How many people die within that year in a population?

Now life expectancy plays into that. Life expectancy is how many years are you supposed to live. So life expectancy in a country like the United States of America-- I don't know the number off the top my head-- but let's just take a blind guess that it's 75 years old is, on average, how old someone should live to or does live you because it's an average in America. And that's going to vary from population to population based at what age people die.

Now another term that goes in with this is infant mortality rate. And what it's really looking at is how many children die in the first year of their life. Infant mortality rate is a part of death rate. So if you die overall, you are going to be in that death rate. But infant mortality's specifically looking at children.

And it can really tell you a lot about what's going on in a certain group because when infant mortality rates are really high, there are some general societal issues that are going on that are keeping that rate high. It can be lack of nutrition. It can be health care issues. It can be disease issues. Many different things it can be, but it's a good indicator when you're looking at populations.

Now emigration is when people move out of an area. So that's when people decide to move away from a group. So if we go back to that formula, now it makes a lot more sense. Population equals, well, we have the number of births minus the number of deaths. And then you have migration. So you have the number of people immigrating versus people emigrating.

So demography is really looking at the structure of human populations. So it's empirically studying populations. And so demographers are really using a lot of those terms I just gave you to look at human population.

So today's takeaway message. Demography, like I just said, is empirically studying the structure of human populations. We looked at fertility and mortality. So fertility is the ability for people or population to have children, and mortality is measuring how often people die in a population. Then we had some different terms looking within those two general things. And so death rate is death rates over a specific time versus birth rate, which is birth rates over a specific time.

Infant mortality is looking at deaths for children under one-year-old. And life expectancy is the average number of years of life for a person in a group. Then migration is people moving people in or out of an area. And again, immigration is people moving in, and emigration is people moving out. Well, that's it for this lesson. Good work. And hopefully, you'll be seeing me on your screen again soon. Peace.

Terms to Know
Birth Rate

A rate of births over a specific time (normally expressed as x per 1,000 people).

Death Rate

A rate of deaths over a specific time (normally expressed as x per 1,000 people).


The empirical study involving the structure of human populations.


The ability to conceive children, which is measured statistically and referred to as birth rates.

Infant Mortality Rate

A rate of deaths of children under 1 year old over a specific time (normally expressed as x per 1,000 people).

Life Expectancy

The average years of life for a person within a group or population.


Movement of people into or out of an area.


Measuring how frequently death occurs in a given population.