Did the Northern Mariana Islands Experience a Baby Boom?
How Fertility Statistics Can Mislead
I was recently expanding my demographic knowledge of U.S. territories and ran across a weird factoid: from 2000 to 2010, the total fertility rate of the Northern Mariana Islands rose dramatically. What explains this rise? Such a huge increase is unusual, especially given that population on the whole was declining.
So let’s back up a bit. What are the Northern Mariana Islands?
That green dot is where the Northern Mariana Islands are located, just north of Guam, northwest of the Federated States of Micronesia, northeast of Palau… okay yeah those directions aren’t helpful.
Basically, it’s way out in the Pacific, a lot closer to Asia than to Hawaii, and certainly closer to Asia than to the mainland United States.
Northern Mariana Islands is a U.S. territory. This means islanders are United States citizens by birth, and it means they have non-voting representation in Congress, but they have special taxation and spending rules similar to Puerto Rico. However, while Puerto Rico has almost 3.5 million people, the Northern Mariana Islands have just over 50,000. In fact, here’s a graph of territorial populations other than Puerto Rico:
As you can see, the Commonwealth of the Northern Mariana Islands (CNMI henceforth) is close to the least populous U.S. territory, competing with American Samoa. It had a massive population boom in the 80s and 90s, then a decline afterwards.
Here I want to mention an interesting factoid related to Puerto Rico. Below is the population density of U.S. territories.
That’s people per square kilometer. Puerto Rico is one of the most densely-populated places in the entire United States, but, whereas most dense states are very rich, Puerto Rico is very poor. When we think about Puerto Rico’s population, “density convergence” is not a terrible model to use.
Anyways, back to CNMI, you can see that it has the lowest population density… but it would still be the 8th densest U.S. state. So these are very high densities, created by the nature of island living.
But what caused CNMI’s decline?
Well, we can look at Census data back to 1980 for a clue.
Look at that Asian line! Yes, the 80s saw growth for every group, but they really saw growth for Asians, particularly Chinese and Taiwanese. But then after 2000, the Asian population began to shrink rapidly, and by the mid-2000s, the other racial groups were too. What happened?
Well, from a high of 36 garment factories in the late 1990s, by 2009 every garment factory in CNMI was gone. These factories were largely Chinese-owned, recruiting Chinese workers, particularly young women, and they were housed in shared housing.
With that in mind, let’s look at some fertility data. Here’s Census-bureau-estimated total fertility in CNMI:
Now this is where it gets interesting. Between 2000 and 2010, the Chinese population falls from over 15,000 people, to just 3,600. Meanwhile, we can expect that large groups of single, young Chinese women housed corporately may boost total births somewhat, but, being single, corporately housed, and coming from a low-fertility culture, these women probably had low total fertility. Sadly, I can’t find microdata on fertility by race for CNMI in 2000 or 1990. But I can get it for 2010. Here’s children-ever-born by race and age in 2010:
As you can see, Islanders (the blue lines) have the highest fertility for all ages, while Asians (red lines) have much lower, particularly Chinese women.
Well, that means that if the composition of the population changes, so should fertility! And boy-howdy did the population composition change!
Using 2010 data, I will guesstimate historic race-specific total fertility, apply it to the historic size of each racial group, and then aggregate these to get an implied historic fertility rate. I will use documented completed fertility to help estimate historic years.
As you can see, my method understates the change, but nonetheless shows that the decline in Chinese population alone can explain a large share of the fertility increase. My bias is to think it can explain 100% of the fertility increase, but I’ll admit I haven’t proven that. For what it’s worth, I show slightly falling islander fertility during this period of around 3 children per woman, and roughly stable “Other” fertility just below replacement.
But this is a really fascinating case where population decline boosted observed fertility despite possibly no change in any individual subgroup’s fertility, simply by changing the composition of the population. In other words, this fertility increase would be unlikely to increase population forecasts, because it is no change in any actual group’s fertility.
I have no big takeaway for this post, just wanted to offer readers a fascinating tidbit about the Northern Mariana Islands, and, ultimately, a case study in how migration can impact fertility.
Check out my Podcast about the history of American migration.
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I’m a native of Wilmore, Kentucky, a graduate of Transylvania University, and also the George Washington University’s Elliott School. My real job is as an economist at USDA’s Foreign Agricultural Service, where I analyze and forecast cotton market conditions. I’m married to a kickass Kentucky woman named Ruth.
DISCLAIMER: My posts are not endorsed by and do not in any way represent the opinions of the United States government or any branch, department, agency, or division of it. My writing represents exclusively my own opinions. I did not receive any financial support or remuneration from any party for this research.
