The Internet had a conniption last week when Jeb Bush spoke at the Faith and Freedom Coalition Conference and made the following remark:

Immigrants create far more businesses than native-born Americans. Immigrants are more fertile, and they love families, and they have more intact families, and they bring a younger population. Immigrants create an engine of economic prosperity.

People on both the left and the right did not like this statement. Not. One. Bit.

Bush deserves, I think, something of a defensplanation. (Meaning: Not quite a defense; not quite an explanation.) So let's unpack Jeb’s statement piece by piece.

I can't speak to business creation rates. If Bush says that immigrants create more businesses than native-born Americans, then I assume he has data to back up his claim. However, it's not clear if he's talking about the absolute number of businesses created or the rate of entrepreneurship. But I suspect it's the latter for the following reason: Levels of entrepreneurship tend to be greater in the younger segments of the population. And Hispanic Americans—a large number of whom are recent immigrants—have a much lower median age than the general U.S. population. The median age in America is 37; the median age for Hispanic Americans is 27.

Now, this number includes both native-born and foreign Hispanic Americans. And Jeb was talking about foreign-born populations in general, not just Hispanics. But since we're just doing rough, back-of-the-envelope calculations, you can see why this claim is plausible.

Jeb also says that immigrants love their families, which seems perfectly sensible. He also says they have more intact families; this is a little harder to adjudicate. I'll just take one metric for "intact families"—percentage of non-marital births. The Census Bureau's most recent report on birth data says that 23.6 percent of all births to foreign-born women in America are to single mothers. For natives, 38.8 percent of all births are to unwed mothers. There are other metrics you might use to measure "intact families," but this one supports Jeb's claim. What may have confused some people is the difference between foreign-born births in particular, and Hispanic-American births in general. (Forty-three percent of Hispanic-American births are non-marital, which is higher than the national average; but this includes both foreign-born and native-born Hispanic Americans. But to make matters more confusing, that’s from the Census Bureau’s 2011 ACS, which is a survey and not a hard count. The data from the 2010 Vital Statistics Report, which actually analyzes every birth certificate in the country, puts the non-marital birth rate for Hispanics at 53.4 percent. Lies, damned lies, etc.)

Bush closed by saying that immigrants are "engines of economic prosperity," and this is outside my wheelhouse, so I'll leave it alone.

But what really got Jeb in trouble was saying that immigrants are "more fertile."

"Fertile" is wrong. I'm unaware of any research that suggests immigrants have an easier time conceiving, which is what "fertile" means. But everyone knows (or should know) that Jeb simply misspoke. He was talking about the fertility rate.

The total fertility rate, or "TFR," is a statistical construct that attempts to measure how many babies women in a given population set would have in their lifetimes, if all of these women survived through the end of their childbearing years. TFR isn't a particularly hard number—it's really an estimate for a given snapshot in time. (If you want really firm numbers, you’d rather look at "completed cohort fertility," which measures how many babies women in a given age-range actually had during their lifetimes.) But TFR is quite useful for understanding the broad contours of fertility behavior, and on this score, Jeb is exactly right: Foreign-born immigrants have higher TFRs than native Americans.

When you step back from the TFR and look at cruder measures, such as the birth rate—which is just the number of babies born for every 1,000 women between the ages of 15 and 44, you see basically the same picture: Foreign born women have a significantly higher birth rate (87.8) than native women (58.9).

So as a factual matter, what Bush said is unremarkable.

That said, there are two bits of nuance on immigrant fertility that are worth noting.

First, the women who immigrate to America tend to have high fertility rates even by the standards of their home countries. For example, back in 2002, Mexican women had a TFR of 2.4. But Mexican women immigrating to the United States carried with them a TFR of 3.5—meaning that the women leaving Mexico were on the right side of their country's fertility bell curve. The same was true for Canadian immigrants. Canada's TFR average was 1.5; Canadian immigrants to the United States had a TFR of 1.9.

Yet this phenomenon isn’t universal. Immigrants from China, Korea, Cuba, El Salvador, and the U.K. all had fertility rates higher than the average of their home countries. But immigrants from the Philippines, India, and Vietnam came with much lower fertility rates than the average of their sending countries.

Interesting, no?

The more salient fact, however, is that once women come to America, their fertility rates rush back toward our national average at a brisk clip. From 2007 to 2010, for instance, the birth rate for native-born American women declined by 6 percent. The birth rate for foreign-born women declined by 14 percent—more than twice as fast.

I mention all of this because it's worth having as full an understanding of the demographics of immigration as possible.

Now, Bush was highlighting the demographic benefits of immigration in pursuit of a crudely political argument—he wants the Senate to pass the current immigration bill in order to move toward legalization for the 11 or 12 million illegal immigrants currently in America, the vast majority of whom are from Central and South America, particularly Mexico.

And on this subject, it's not clear that Bush’s statement is particularly germane. It's perfectly sensible to argue that the mass immigration we've received over the last 35 years has been a blessing—a mixed one, but a blessing just the same. Yet that has almost nothing to do with the very narrow question whether or not we pursue what amounts to amnesty for a subset of the immigrants who are in the country illegally.

The demographic benefits of immigration are what we should consider in crafting forward-looking policy concerning the system that regulates our immigrant inflows. But that system is separate from the political question of whether or not we should be moving to amnesty the illegal immigrants already in the United States. Because those folks are already here, whether they're eventually amnestied or not. And whether or not we give them amnesty has nothing to do with the extent to which we allow for more (or less) legal immigration in the future.

One final, niggling statistical note: Jeb also said that immigrants "bring a younger population." Again, that's factually accurate; the average age of the foreign-born population is lower than the native-born average. (Though even that is a little hard to get at and requires creative accounting for the native-born children of foreign-born immigrants.) But the real question we worry about in demographics is a society's age-profile. And for complicated mathematical reasons, immigration does not necessarily make a country more youthful; in fact, in certain circumstances it can make a society even older and grayer. Anyone who's a glutton for complicated math can read Carl Schmertmann’s 1992 treatise on the subject. But don't say I didn't warn you.

Jonathan V. Last is a senior writer at The Weekly Standard and the author of What to Expect When No One’s Expecting: America’s Coming Demographic Disaster (Encounter).

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