May 5, 2008

Answering George on Low Birth Rates in the West

George Carty has (once again) asked an interesting question, this time in response to my Straight Talk About Islam post:

About the birth rates thing - do you think that environmentalist propaganda about "overpopulation" has anything to do with low birth rates in the West?

For a number of years, I've argued that declining birth rates more often had to do with increasing standards of living. The higher the standard of living, the lower the birth rate. I had argued that this could be seen as far back as the era of Augustus, with his introduction of laws such as the Lex Papia Poppaea, which penalized the celibate and childless, especially among Rome's patrician class.

Caesar Augustus encouraged marriage and having children. He assessed heavier taxes on unmarried men and women and, by contrast, offered rewards for marriage and child bearing. Since there were more males than females among the nobility, he permitted that anyone who wished (except for senators) to marry freedwomen could do so, and decreed the children of these marriages to be legitimate, (Suetonius). (Source)

And so I did a quick-and-dirty analysis using data from the CIA World Factbook to see just how true this proposal might be. Using GDP per capita on a purchasing power parity (PPP) basis as a proxy to measure the standard of living, I compared that statistic against total fertility rates for a total of 221 countries. A graph of the data points can be seen below:

On the X-axis we have the total fertility rates with a minimum of 1.00 (Hong Kong) and a maximum of 7.34 (Mali). On the Y-axis we have GDP per capita. If my idea is correct we should expect to find the numbers running from the top-left to the bottom-right. We do see this somewhat, although with a lot of data points in the lower left corner (low total fertility rates and low GDP per capita). If my original idea was correct, the correlation coefficient, which measures the strength and direction of two sets of related data, would be close to negative 1, which indicates a perfectly negative relationship between the two data sets (in other words, the higher one set of data is, the lower the other data set is). Here, the correlation coefficient is negative 0.4854. So there is a negative relationship, but of middling strength.

I also remembered seeing some statistics before showing that countries with low life expectancies often had high birth rates. (If you know that you're likely to die at a young age, you're not likely to wait around until your thirties or forties before having kids, like in Western cultures.) So I took the total fertility rates and compared it against the life expectancies at birth, also for 221 countries. The graph can be seen below:

Now here is a more negative relationship that's much more clearly defined. The correlation coefficient confirms this, being at negative 0.7678, which is much stronger than the correlation coefficient for GDP. In other words, the longer people live, the less likely they are to have children. This is perhaps more of a reflection of a country's ability to provide better health care to their citizens: the better a country's health care, the lower the country's population growth rate. However, there are exceptions to this rule as well. For example, some of the countries with higher life expectancies and total fertility rates tend to be Muslim countries, like Oman (73.91 years; 5.62 babies/woman) and the Gaza Strip (72.34 years; 5.51 babies/woman). Likewise, there are some countries who have both low birth rates and low life expectancies. But, overall, life expectancy seems to be a better explanation why Western cultures have lower birth rates, at least in comparison to standard of living. (There are a couple of other analyses that could be done as well; e.g., life expectancy of men vs. women, and multiple regression analysis of GDP per capita and life expectancy vs. total fertility rates, but I'll save those for the future, insha'allah.)

And, obviously, to answer George's original question, no, I don't think overpopulation has much to do with Western birth rates, although that could be an analysis for another day.

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