Measurements of Fertility: Terms, Calculations & Interpretations Video

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  • 0:48 Crude Birth Rate
  • 1:33 General Fertility Rate
  • 2:37 Total Fertility Rate
  • 3:35 Gross Reproduction Rate
  • 4:29 Net Reproduction Rate
  • 5:34 Lesson Summary
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Lesson Transcript
Instructor: Christopher Muscato

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

In this lesson, explore five different measurements of fertility and discover how each is calculated and used. Then, test your understanding with a brief quiz.

Measuring Fertility

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.

Crude Birth Rate

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.

General Fertility Rate

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.

Total Fertility Rate

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.

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