Back To CourseSociology 104: World Population
8 chapters | 88 lessons
As a member, you'll also get unlimited access to over 75,000 lessons in math, English, science, history, and more. Plus, get practice tests, quizzes, and personalized coaching to help you succeed.Try it risk-free
Chris has a master's degree in history and teaches at the University of Northern Colorado.
This is the world. You probably recognize it. Within this world are people. Lots and lots of people. After years of research, social scientists have realized that all of these people have to share this world. Until we colonize Mars, this is all we've got. This much space, this amount of resources, this is the world we have to share. Now, in order to make sure that we have enough to go around, researchers started calculating rates of fertility, or birthrates, so that we can predict how many people are going to be sharing this world. After all, sharing is caring. Turns out, calculating fertility rates is caring, too.
So, how exactly do we calculate fertility rates? There are a number of ways we can look at this. One of the most basic is the crude birth rate (CBR), the number of live births per 1,000 people in a population during a single year.
This is easy to calculate. It just involves going through statistical data from censuses and other sources and counting the number of live births, then expressing that as a ratio out of 1,000 people. It looks like this: (Total Births / Total Population) x 1,000. For example, as of 2014, the CBR of the United States was 13. So, within every group of 1,000 people there are an average of 13 babies born every year.
The crude birth rate is, well, crude, because it is such a rough estimate. For a slightly more accurate prediction, we could use the general fertility rate (GFR), which is the number of live births per 1,000 women of reproductive age in a year. See the difference? While the CBR calculates a ratio of live births by the entire population, the GFR takes into account the fact that only a certain group of people will be actually having children. For statistical purposes, a woman is considered to be within reproductive age if she is 15-49 years old. That's the population that is statistically actually able to have children, so to get a more accurate fertility rate we only need to look at this population.
The formula looks like this: (Total Births / Total Women age 15-49) x 1,000. Here in the USA, the general fertility rate as of 2014, was right about at 62.5 live births per 1,000 women of reproductive age.
For an even more accurate estimate, we'll have to put in more work. The total fertility rate is the average number of children that a woman would have if she survives to age 50. This estimate requires making a few other calculations. First, you have to determine the average fertility rate for every group of women within a 5-year range from 15-49. So, say that women 15-19 have a certain fertility rate, then women 20-24 have a different fertility rate, etc. By doing this, you build up a chart of fertility rates across the entire reproductive age and then you assume that women born in that year will follow those same trends throughout their lives. This helps you predict their future fertility. As of 2014, the total fertility rate in the USA, the total number of children the average woman is expected to have throughout her life, is 2.01.
Now, so far we've looked at fertility ratios that take into account the fact that only women give birth in a population, but none of those take into account that only their daughters will as well. That's what the gross reproduction rate (GRR) does; it calculates the average number of daughters that a woman would have if she lived to age 45. This average is based on the current sex ratios, the number of men to women in a population. The idea is that if a generation of women has x number of daughters, those daughters represent the next generation responsible for future fertility rates. So, by predicting how many daughters a woman will have, you predict what future fertility will look like. As of 2014, here in the USA, the GRR is sitting at 1.01, meaning that the average American woman will have 1 daughter by age 45.
Okay, we've got time for one last measurement. The net reproduction rate (NRR), just like the gross reproduction rate, calculates average number of daughters born to a woman but instead of estimating that number to age 45, the NRR calculates this in terms of average mortality rates. Basically, it recognizes that some women will not survive throughout their reproductive years. Generally, this lowers the average number of daughters slightly, since we are now taking into account the average number of women who will die before reaching age 50. In some places, especially those with poor healthcare, this can make a big difference. In the USA, it's not quite that drastic. As of 2014, our net reproduction rate was right at about 0.95, or just under one daughter per woman. So, what does that mean? Well, it means that there will be slightly fewer women in the next generation than this one, which means that fertility rates should go down.
This world is all we've got, so it's important to be able to estimate just how many people will be living here. Fertility rates, or birth rates, are a great way to do this. But, how do we measure fertility rates?
One option is the crude birth rate, the number of live births per 1,000 people in a population during a single year. For a more specific measurement, there's the general fertility rate, which is the number of live births per 1,000 women of reproductive age in a year.
This can be examined even more specifically with the total fertility rate, the average number of children that a woman would have if she survives to age 50.
Predicting the future also requires thinking about future female populations, and for that we can turn to the gross reproduction rate, the average number of daughters that a woman would have if she lived to age 45.
The last measurement we can use is the net reproduction rate. Just like the gross reproduction rate, it calculates average number of daughters born to a woman, but instead of estimating that number to age 45, the NRR calculates this in terms of average mortality rates.
Each of these measurements requires slightly different calculations, but with them we can get a glimpse of our future - and just how many people we'll be sharing that future with.
To unlock this lesson you must be a Study.com Member.
Create your account
Already a member? Log InBack
Did you know… We have over 160 college courses that prepare you to earn credit by exam that is accepted by over 1,500 colleges and universities. You can test out of the first two years of college and save thousands off your degree. Anyone can earn credit-by-exam regardless of age or education level.
To learn more, visit our Earning Credit Page
Not sure what college you want to attend yet? Study.com has thousands of articles about every imaginable degree, area of study and career path that can help you find the school that's right for you.
Back To CourseSociology 104: World Population
8 chapters | 88 lessons