Bryan Caplan  

Rojas on Selfish Reasons to Have More Kids

NCAA Outcomes: Margins and Ra... I Thought I was Being Civil...
Fabio Rojas, sociology professor at Indiana University and my best friend from UC Berkeley, reviews my new book at Orgtheory.  His more than fair intro:
Though this book is written by an economist, it's not another cute-o-nomics pop text. It's a serious book about family planning that's based on his reading of child development, psychology, genetics, economics, and other fields. It's about one of life's most important decisions, and this is what social scientsits should be thinking about. The argument boils down to a simple point. If the evidence shows that you are over estimating the cost of having children, then, on the margin, you should probably have another child.
Fab then seems to criticize me for overstating my case:

In my view, twin studies tend to have two important limitations. First, there is non-random selection of parents into adoption. Adopters are, by definition, very unlike the rest of the population. Not in income or demographics, but in personality...

The other limitation of twin and adoption studies is that they study variation in existing parenting practices. It may be the case that American parents simply don't know how to correctly socialize a kid to reach some goal. Therefore, variations in family environment are just variations in failed practices.

Here's a concrete example: child obesity. A hard core twin study advocate would justifiably point to twin studies showing that weight or BMI is more linked to shared parents than shared family environment... To be blunt, in a world where *everyone* eats bags of twinkies, there won't be much of an effect of living in a home where people eat a few more or less twinkies.

For that reason, it is too much of a jump to say that family environment can't possibly affect weight. For example, parents who remove all twinkies and switch to an all broccoli diet will likely affect their children's weight.
What disappoints me about Fab's criticisms is that I specifically address and agree with virtually all of them in the text of the book.  I repeatedly state that the best way to interpret the adoption evidence is, "If you're fit to adopt, you're good enough."  And I repeatedly disavow the view that that "family environment can't affect X."  All I ever claim is that family environment doesn't affect X (or has little effect on X).  I devote entire sections to the latter point.  So why does Fab write "Even if the argument is overstated" as if these sections didn't exist?

Admittedly, if First World parenting were extremely homogeneous, mere disclaimers might not be enough.  But by almost any standard, parenting in the U.S. is diverse.  We've got the whole range from fundamentalist to hippie, health nut to McDonald's "heavy users," ghetto poor to millionaire, TV-always-on to no-TV-at-all, Ozzie-and-Harriet to Rachel Berry's "two gay dads."  Twin studies often undersample the poor, but not severely.  Current adoption samples are fairly restrictive, but many of the best studies - like Sacerdote's work on Korean adoptees - look at kids adopted when the rules were much more lax.  And Scandinavian twin and adoption studies are often based on national registries where sample bias isn't an issue.

At risk of pedantry, I'd really like Fab to re-read pages 41-42 and 83-86 and tell me how I failed to anticipate the key complaints in his review.  How about it, old friend?

COMMENTS (8 to date)
David O writes:

Why exactly do you place scare quotes around "two gay dads"?

Garrett writes:

Maybe it's trademarked.

david (not henderson) writes:

I really take issue with what's implied here:

"parents who remove all twinkies and switch to an all broccoli diet will likely affect their children's weight"

See, for example:

We need to get past these stereotypes.

Vince Skolny writes:

It's not a stereotype, David, because people that feast on junk food don't scrupulously restrict calories. Nor do they assure their protein intake and nutrient level.

That's why they're obese, like Haub was obese.

Like a market, the human body tends toward equilibrium sans interference and it takes consistent work-- the kind the Twinky eaters do-- to remain obese.

Losing a lot of weight quickly via calorie reduction is the simplest thing in the world.

Even at his new weight, Haub's 1800 calorie-per-day diet is only slightly more than 10 calories per pound, which is exceedingly low.

So low, in fact, that if he keeps it up, his body will conserve the fat he has left and begin metabolizing muscles.

In fact, if you do the math, his lean body mass fell from 134.67 to 132.24 for exactly the reasons I cited.

It's why many people with poor eating habits are "skinny fat"-- no muscles and spare tires.

The kind of pop science you're siting is useful for helping people excuse poor eating, but little more.

And, even if you were right, it doesn't negate Bryan's point, because replacing Twinkies with broccoli will cut calories-- and in a much more sensible way than Haub-- which is the very point you're trying to raise.

The difference is you can gorge on broccoli (like fat people gorge on Twinkies, pizza, and McDonald's) and not get fat.

Bryan Caplan writes:

@David - Those aren't scare quotes, but normal quotes. That's how Rachel always refers to them.

Brian A. Pitt writes:

Bryan Caplan, Fabio Rojas, and Michael Huemer: One will have to become brilliant with just one of three of these guys as an undergrad buddy.

Christian Galgano writes:

Written in jest (and probably with spelling/grammatical errors of my own):

Studying and then working in an academic environment may not be a cure-all for the effects of the similiarity heuristic in common spelling errors, "On another level, I feel that twin and adoption studies can be pushed to far because twin and adoption studies have a very powerful, but very specific, research design" (Rojas). I playfully point out how Professor Rojas wrote "to" instead of "too," because (most?) everyone else makes spelling errors like these from time to time. At what point is it reasonable to assume that elementary school students and college professors incorrectly write "to" instead of "too," because of an innate cognitive bias for mistaking similar words and not variation in academic environment? Adoption/twin studies are the gold standard for separating the effects of nature vs. nurture, and if these studies have ample and sufficient variation in family environment, as Professor Caplan reports, then the burden of proof for critiques of these studies' conclusions (and Professor Caplan's conclusions in his book) is on critics presenting more compelling, contradictory evidence--not doubting what the experts say and the data show in spite of the evidence.

Bill Dickens writes:

"And Scandinavian twin and adoption studies are often based on national registries where sample bias isn't an issue." Not true Bryan. People were invited to take part in the study from a national registry, but participation was voluntary and we know that voluntary participants in scientific studies tend to be both richer and more highly educated than the public as a whole. If you can find evidence to the contrary I would love to see it. I'm doing a meta analysis of these studies and my RA has been unable to obtain data on the representativeness of the Scandinavian samples.

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