That peer effects still seem like they would be important is a fair point. The question is: if peer effects are important, why don't they show up in adoption studies? Perhaps parents don't think peer effects are important, but that seems implausible to me. Perhaps, as you suggest, it's really expensive to affect your childrens' peers. But then that fits Caplan's argument pretty well; if if you have to spend millions of dollars to change your childrens' peers then maybe it's just not that cost effective, and you shouldn't worry about it too much.

As a side note: I sometimes get a very "politics" vibe from your comments, and it gives me the impression that your thought quality isn't very good on those topics (other comments good quality). I don't know if others get the same feeling from your posts; maybe it's just me.

For example, "enormous debt, which you won't be able to pay off for decades, and living a stressful and anxious existence on the edge of solvency, in which a fit of bad luck can easily send you into ruin. And this latter possibility doesn't mean just falling back to a more frugal but still respectable lifestyle -- it means being thrown, together with your kids, right into the dreaded underclass in which all sorts of frightful social pathologies are rampant. It's like precariously holding onto a rope above a pond full of crocodiles." reads a lot like standard political rants.

The question is: if peer effects are important, why don't they show up in adoption studies?

Generally speaking, when I search for literature on peer effects, the information is sparse and confusing. I'm not too surprised, since such effects are much more difficult to disentangle than heritability and shared environment.

My working hypothesis is that:

  1. Peer effects matter a lot, but only up to a certain threshold of peer quality, and this threshold is basically what people intuitively perceive as sufficiently respectable company for their kids. So, basi

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Review: Selfish Reasons to Have More Kids

by jsalvatier 3 min read29th May 2012260 comments

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This is a review of Bryan Caplan’s book Selfish Reasons to Have More Kids. Co-written with Walid.

Summary

Adoption studies indicate that differences in parenting styles have mostly small impacts on long term life outcomes of children, such as happiness, income, intelligence, health, etc.. This means that parents can put less effort into parenting without hurting their children’s futures. If you think kids are neat, then you should consider having more. 

Review

Note: We think this is a pretty useful book, and it has changed our minds on how many children we want to have, though neither one us has any children yet. Also, neither of us are experts on twin or adoption studies.

Caplan argues that parents drastically overestimate their ability to improve the adult lives of their children. His argument is driven by adoption studies, which suggest that there is very little that parents can do beyond techniques employed by the average parent that would get them better results with their children. Specifically, the following areas are identified as areas where differences in parenting don’t seem to matter:

  • No effect on life expectancy, overall health (as measured by the presence/absence of particular health problems and self reported health), height, weight or dental health.
  • No effect on intelligence.
  • No effect on various measures of personality: conscientiousness, agreeableness or openness (not certain about extroversion or neuroticism).
  • Little or no effect on marriage, marriage satisfaction, divorce, or child bearing.

But that is not to say that styles outside of the average do not matter at all -- there are a few areas where parenting differences do seem to have an effect:

  • A small effect on adult drinking, smoking and drug problems.
  • A small effect on educational attainment, but no effect on grades in school or on income.
  • A large effect on political and religious labels, such as whether you call yourself democrat or republican or Christian or Muslim but small effects on actual political and religious attitudes or behavior.
  • A moderate effect on when girls start having sex (but not boys), but no effect on teen pregnancy or adult sexual behaviors. 
  • Possibly a small effect on sexual orientation.
  • A moderate effect on how children remember and perceive their parents.

So how do adoption studies lead to these conclusions?

Adoption studies (If you have a link to a better overview or discussion of adoption studies, we'd appreciate it) help find out the influence of parenting differences on adult outcomes by comparing adoptees to their adopting family. If adoptees systematically tend to be more like their adopting family than like other adoptees along some measure (say religiosity or income), that implies that parenting differences affect that measure.

When an adoption study finds that parenting does not affect outcome X, it does not mean that parenting cannot affect it, just that the parenting styles in the data set did not affect it.

The evidence Caplan talks about is primarily long run life outcomes. Shorter run life outcomes often do show larger effects from parenting, but these effects diminish as the time horizon increases.

If parenting doesn’t matter, what does?

Caplan references twin studies in showing that genetics have relatively big effects on all the measures previously mentioned. This explains why we see strong correlations between parents’ traits and children's’ traits. He specifically uses it to call out attributes that we would commonly ascribe to parenting, but may actually have a much larger genetic component.

Implications

Once Caplan has argued for the stylized fact that parenting has only small effects on major life outcomes, he explores some of its implications. 

Don’t be a tiger parent

One big implication is that you should put less effort into trying to make your kids into great adults and more effort into making your and your kids’ lives more fun right now.

For example, parents probably spend too much energy convincing their children to eat their vegetables and learn the piano, given that it won’t affect whether they will eat healthy as adults or be more intelligent. No one likes fighting. If you want your kid to learn the violin so they’ll have fun right now, it may very well be worth it, but don’t do it because you think it will increase their future income or intelligence. If neither you nor your child likes doing an activity, consider whether you can stop doing it.

Adoption studies provide good evidence that most activities don’t have a much of a long term effect on your children, so you need good evidence to start thinking that an activity will be good for your kids future. The odds are against it.

Have more kids

Focusing more on making your and your children’s lives more fun means that overall, having kids should be more attractive. If having another kid no longer means fighting about finishing their broccoli every night, maybe it’s not such a bad idea. On the margin, you should consider having more kids. If you were planning to have zero kids, consider having one. If you were planning to have 3 kids, consider 4, etc.

Other Topics

In much of the rest of the book Caplan gives common sense advice for making parenting easier for the parents. A couple of these, such as the Ferber method for dealing with infant sleep problems, are empirically based.

Here are some other topics Caplan discusses in his book:

  • Happiness research on parenting. Caplan argues that although being a parent seems to make people less happy, the effect is small (Ch 1).
  • Child safety statistics. Children are many times safer than in decades past (Ch 4).
  • Many of the benefits of having children come later in life (e.g. having people who will come and visit you, etc.), which makes it psychologically easy to ignore these benefits (Ch 5).
  • The externalities of children. He argues that on net, extra people have large positive externalities (Ch 6), so you shouldn’t feel guilty for having more children.

What parts should I read?

We wholeheartedly recommend reading the first 5 chapters (121 pages) of Selfish Reasons To Have More Kids as these have the most useful parts of the book; the rest of the book is less valuable. 

Criticisms of Selfish Reason To Have More Kids

There are a number of criticisms relevant to Caplan’s arugments. For example:

  • Nisbett claims that heredity is much less important for IQ than thought (see also counterclaims posted below).
  • Will Wilkinson claims (one, two) that the cost of parenting plays a small role in people's family size decisions, thus it's not a very strong reason to have more kids.
  • Jason Collins likes the book but would like it to discuss the research on non-shared environment (i.e. that not explained by genetic or parenting differences, such as peer effects) (link).  

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