I sent Arthur Brooks, author of the article that I critiqued in my last post, the following email:
Dear Mr. Brooks,
I read with interest your article in yesterday's Opinion Journal titled, "The Fertility Gap". I had one question. In the article, you write:
"Consider future presidential elections in a swing state (like Ohio), and assume that the current patterns in fertility continue. A state that was split 50-50 between left and right in 2004 will tilt right by 2012, 54% to 46%."
I was curious as to how you arrived at these numbers. Taking into consideration fertility, mortality, and the assumption that new births favor conservatives by the numbers you gave (and ignoring the fact that babies have to wait 18 years before they can vote), there should be only a very small change in the split between liberal and conservative (something like 49/51 by my quick estimate) by the year 2012.
Any help you can give on this issue is appreciated. Thanks!
He has responded:
Thanks very much for your note.
The sims on this thing have a lot of strong parametric assumptions, obviously. The way I'm working it is to assume that about an eighteenth of the baby differential comes of voting age each year, that the gap is increasing at the historic rate of about .6 percentage points per year, and that consequently the fertile adult population is getting bigger pretty fast among conservatives. The difference gets even bigger if we include the fact that conservatives from voting families tend to vote more frequently than liberals from voting families, although I left that part out in the simple sims for the column (those things will go into more academic stuff probably).
Of course, there are a ton of intangibles that make it silly to see this as destiny, most notably immigration. A few assumptions about latino voter mobilization for the dems, and the whole scenario inverts. Of course, latino voters might move rightward over the next 20 years--who knows?
Thanks again for your comment.
Really clears things up, doesn't it? Okay, so he is running "sims". That's nice and all, but you don't need to do simulations to get a quick and dirty estimate. As PZ mentions, an 8% shift in just 8 years due to differential reproduction alone is absurd. I might suggest to Mr. Brooks that he scrutinize his simulations more carefully. I'd do it for him, but he hasn't provided enough details.
I think it's nice though that Brooks acknowledges the potential effect of immigration. Too bad he didn't do that in his article, as it would have completely negated his conclusions. But of course he says that immigration is "intangible", whereas all this time I've been laboring under the impression that it can be measured.