Back To CourseSociology 104: World Population
8 chapters | 88 lessons
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Chris has a master's degree in history and teaches at the University of Northern Colorado.
I am a gardener. Like most gardeners, I have a series of tools that help me collect my harvest. And, what do I harvest? Statistics. That's right, I'm a statistics farmer. Sometimes called a demographer, or a person who researches population statistics. But, like a farmer, I watch something grow, I harvest it, and I make it into something: demographic reports. Not as tasty as a carrot, I'll grant you, but very informational.
So, what's this season's harvest? Right now I'm looking at statistical rates of fertility, or birthrates. As a demographer, this is a very important statistical crop because birth rates help us predict future population trends and indicate areas with major health issues. And, of course, we have a few tools to help us collect our data. So, whaddya say? Let's go harvest some numbers.
Here's one good tool we have for measuring fertility. The child-woman ratio estimates fertility rates based on a ratio of children to women of child-bearing age. Basically, here's how it works. You take the number of children under the age of five within a population; this represents the most recent trends in fertility. Then, you divide that by the number of women between the ages of 15 and 49. That's the assumed number of women who are capable of having children. Then, multiply it by 1,000 and turn it into a ratio. So, the formula would look something like this: CWR = (C / W ) * 1,000.
Let's try that out. Here are the stats for a small local village. There are 4,294 children under five, and 10,235 women in between 15 and 49. So, the formula looks like this: CWR = (4,294 / 10,235) * 1,000. I think we'll use a calculator for this one. And, when we plug that in, we find that the CWR, the child-woman ratio, equals 419.5 - that means that there are roughly 420 children born per every 1,000 women.
The child-woman ratio is a very crude statistic, by which I mean it's not the most accurate. If you need to be really certain about exact fertility rates, this probably isn't the best one to use. However, you don't always need to count every single birth. Sometimes you just need a general estimate of fertility rates, and so this formula is a huge time-saver if you're in a position to allow a little room for error. It's also great when working with historical sources. Obviously, you can't go back in time and count every birth personally, so this is a practical way to harvest past fertility rates.
For a slightly more accurate tool, we might turn to an age-specific rate of fertility, which calculates fertility rates only within a specific age group. This formula actually looks very similar. Here it is: ASR = (B / W ) * 1,000. Let's break that down. ASR, of course, is the age-specific rate that we're trying to figure out, B is the number of births to women in an age group, and W is the number of women in that age group.
Now, for these studies, we generally keep age groups within one to five years, and then repeat this formula for the entire fertile population. So, the first age group would be women aged 15-19, then women 20-24, etc., all the way up to a group of women 45-49. So, say that there are 795 births in the first group of 2,954 women. Okay, so we know that B is 795 and W is 2,954. When we plug those numbers in, we see that the age-specific fertility rate for women aged 15-19 is 269 children per 1,000 women.
By comparing this number to the age-specific fertility rates of the other age groups of women, we can look for major trends in this society. Are women having children earlier or later in life? Is it a consistent rate, or does it sharply increase and decrease? So, this is a much more accurate number than the child-woman ratio since it takes into account actual numbers of births, but that also means it takes more time to gather data and analyze the numbers.
Alright, how about one more tool for calculating fertility? This is the marital fertility rate, a ratio of live births exclusively to married women between 15 and 49 years old within a single year. While many fertility ratios simply calculate a ratio based on women within that child-bearing age range of 15-49, this ratio takes into account the fact that in most societies the majority of births will be to women who are married. So, the ratio looks like this: MFR = (B / M) * 1,000. B is the number of births to married women, and M is the number of women between 15 and 49 who are married. Here's what that looks like in practice - it's pretty similar to what we've seen before.
What makes this ratio nice is that it's based on vital statistics, life changes that only have to be recorded once, including birth, death, marriage, and divorce. So, you go through your vital statistics to find the number of babies born to married mothers, then divide that by the number of women who are married. Since most births in a society are to married parents, this gives you a pretty accurate idea of fertility rates within a population, but is a bit less work than the methods that include unmarried women. Really, it's just another tool to help search for statistical patterns. After all, the more we harvest, the more we have to analyze. For demographers, a good harvest is a veritable feast of numbers.
For a demographer, a person who researches population statistics, one of the important areas of analysis is fertility, or birth rates within a population. Fertility rates can reveal a lot about public health, social values, and people's lives. So, we've got a few tools to help us out, all of which create ratios of children born per 1,000 women within a single year.
The child-woman ratio estimates fertility rates based on a ratio of children to women of child-bearing age. This is a very rough estimate, which is sometimes all you need. For more accurate reports, try an age-specific rate of fertility, which calculates fertility rates only within a specific age group. This is a very detailed analysis, which only measures fertility within groups in the same 5-year age range.
Another tool we can use is the marital fertility rate, a ratio of live births exclusively to married women between 15 and 49 years old. This is still pretty accurate, but relies on vital statistics, life changes that only have to be recorded once, so the data is easier to access and compile. With these tools, we can harvest data, analyze it, and create a veritable buffet of statistics.
After reviewing this lesson, you should be able to define and discuss three different statistical methods for measuring rates of fertility.
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Back To CourseSociology 104: World Population
8 chapters | 88 lessons