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I am a very heretical rationalist, because I believe in an effect of parenting on children.
Among relatively homogeneous samples, about half of variation is genetic, while about half of variation is the product of nonshared environment. However, much of nonshared environment may be the product of measurement error: more careful studies suggest, for example, that 85% of variation in personality is explained by genetics and only 15% by non-shared environment, suggesting that a full 70% of non-shared environment is actually measurement error.
Some people conclude from that study that, in fact, nothing has an effect on anything and your entire personality is based on genetics. I conclude from that study that this is not a very reliable test.
It is very very difficult to pick up small effects with unreliable tests. You need a huge sample size to do so. Twin studies don’t generally have huge sample sizes, because there just aren’t that many twins in the world. And even social science studies that don’t have any twins are regularly underpowered, because journals don’t care about statistical power in the same way that they care about p-values.
It definitely looks like we’re in the sort of world where parenting could have effects. Studies of children who grew up in Romanian orphanages have shown that spending more than six months in the orphanages– in which they had inadequate food, poor hygiene, little social or intellectual stimulation, and no love or affection– results in cognitive impairment, autismlike symptoms, and emotional problems. There is a shared environment effect in heterogeneous samples– such as those which include both rich and poor parents– which is presumably not solely because of the salutary effects inherited wealth can have on the personality. If we know that extreme differences in parenting have effects we can detect, and we know that there are lots of small effects we wouldn’t be able to detect even in principle, then it seems to me that we should assume those small effects exist.
Believing in zero role for shared environment also fails to pass the sniff test. Lots of people, I think, will agree that whether or not you talk to your baby might not have any long-term consequences. But the “zero role for shared environment” position requires yourself to commit to the position that all of the following have either zero correlation between siblings or no effect on children’s psychology whatsoever:
- Lead poisoning.
- All other forms of air and water pollution.
- Prenatal nutrition.
- Drinking during pregnancy. (Not just light drinking, I mean slamming down ten shots a night every night for your entire pregnancy.)
- Smoking during pregnancy.
- Illicit drug use during pregnancy.
- Secondhand smoke exposure during childhood.
- Childhood nutrition.
- Childhood sleep deprivation.
- School quality.
- Whether there are drugs being sold in front of your house.
- Childhood mental health treatment.
- Childhood physical health treatment.
Sure, maybe you can quibble about one or another of these. Maybe you think that sending your kid to Andover will result in exactly the same consequences as sending your kid to a school where they learn that evolution is a lie because the Loch Ness Monster is real. Maybe you think there’s no real harm in feeding your child lead paint for dinner and that fetal alcohol syndrome is a lie made up by people who just want you to stop having fun, man. Maybe you think no one ever smokes through more than one pregnancy. But it seems really implausible to me that every single one of those either doesn’t have an effect or isn’t correlated between siblings.
People who don’t believe in shared environment sometimes propose mechanisms for what non-shared environment is. “Maybe siblings have different friends!” they say. Okay, and your claim is that there is literally zero correlation between who siblings are friends with? No parents ever bring all their children to another child’s house for a shared playdate? Poorly funded inner-city schools contain exactly the same set of people to be friends with as wealthy schools in the suburbs? “Parents treat different children differently!” they say. Okay, and your claim is that there is literally zero correlation between how parents treat one kid and another kid? No similarities based on a parent being a really angry person, or a really demanding person, or a single mom working three jobs who barely has time to take care of herself let alone a child?
The only reasonable course here is to grant “okay, maybe lead poisoning might increase criminality, and children who grow up in a house with lead paint are more likely to have lead poisoning than other children.” That opens the door for other small effects of parenting as well.
The interesting consequence of this argument, however, is that we don’t have much scientific evidence what the good forms of parenting are. There are few randomized controlled trials of parenting strategies. You can do an encouragement design, in which some parents are given free Baby Einstein videos or sent to educational classes about how you shouldn’t spank your children. Unfortunately, since many parents won’t change their behavior even with a class or a free video, you have to have a huge sample size, which is very expensive. So most people just do observational studies, which are cheaper.
Essentially all observational studies of parenting strategies suffer from healthy user bias. The sort of people who follow parenting advice are different from the sort of people who don’t follow parenting advice. They’re more conscientious. They put more effort into parenting. They care about doing right by their children. If nothing else, they’re more likely to follow all the other parenting advice, and that includes obviously correct things like “don’t let your child eat lead paint.” It’s very difficult to control for all of these factors. So if a study finds that following conventional parenting advice makes your child healthier, more talented, and kinder, it doesn’t actually tell you a heck of a lot. (On the other hand, if a study tells you that not following conventional parenting advice makes your child healthier, more talented, and kinder, you should probably listen to that study.)
One heuristic I’ve been using is thinking about the effects I can expect to have on my spouse. There are a lot of similarities: we live together, we spend a lot of time together, and we’ll do so for years. I think our intuitions about our effects on our spouses are less biased than our intuitions about our effects on our children, because we don’t have a ridiculous guilt-inducing culture that believes that if we just do everything right any spouse can make a six-figure income, live to age 100, and be ecstatically happy at all times. These are my intuitions about my spouse:
- My husband’s basic temperament is set. He is always going to be basically himself, no matter what I do.
- I have a huge effect on how much my husband likes me and how good our relationship is.
- I could traumatize him if I chose to behave in an unconscionable way.
- I definitely have it in my power to make my husband miserable, but it’s not in my power to make my husband happy– brain chemistry and other life influences have their role.
- I am only one influence on my husband’s behavior. The effect of my actions is real, but I cannot automatically cause anything to happen.
- I can share information with my husband that changes his behavior.
- I can model behaviors I’d like my husband to pick up. If my husband sees me exercising, he’s more likely to exercise himself.
- I can reward my husband for doing things I want him to do, but I shouldn’t expect that he’d keep doing the thing if I stopped rewarding him.
- I can introduce my husband to experiences he otherwise wouldn’t have but that he enjoys.
- I can support my husband and allow him to achieve things he wouldn’t be able to otherwise.
- None of those five things work 100% of the time. How well they work on any given subject depends on my husband’s preferences, temperament, and choices.
- Perhaps most of the effect I have on my husband’s personality does not come from my deliberate efforts. It comes from how he responds to my everyday behaviors.
- If we stayed married for twenty years and then he divorced me, I’d expect my effects on his personality to decrease over time, but there’d always be an effect that came from me.
Of course, children and spouses are different in many ways. For one thing, not loving an infant causes far worse long-term consequences than not loving a spouse. But I think as a first-pass heuristic for what effects you can and can’t have, and how you can have them, this is pretty reasonable.
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gazeboist said:
On what? This mystery will haunt me.
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notpeerreviewed said:
One of my uncles, as a child, slept in the same basement where his father cast homemade, hobbyist bullets out of molten lead. His overall life outcomes have been much, much worse than those of his two siblings. That would show up as “nonshared environment” in a twin study, even though it’s a household-specific effect that’s clearly due to bad parenting.
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notpeerreviewed said:
The other two siblings didn’t sleep in the basement, in case that wasn’t clear.
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Moriwen said:
Great post — and I agree, yeah, all seems very plausible.
The mathematician in me is coming up with trivial cases of parenting having effects on children. It can obviously have effects on your children *right now*, even if they dissipate over time. If someone murders their child, I’m pretty sure that’s going to have an effect on the child’s life outcomes.
Only point of disagreement: if a study says doing something not generally considered good parenting has good effects, I’m a lot less likely to listen than to go “huh, wonder how they messed *this* one up.”
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Protagoras said:
One of the reasons so many social science studies seem to have problems is that confounders are immensely difficult to identify and correct for in phenomena as complex as human behavior. A lot of rationalists seem to assume that this hasn’t been a problem for the studies into genetic influences; often this seems to be because studies on genetics get politically incorrect results, and at least some of the right-leaning rationalists blame the problems in social science on politically motivated researchers. But if (as seems to me to be the case) the confounders are more of a problem than politics, there’s no reason to think research into genetic influences will have very much less of the problems that have produced the replication crisis. So I don’t think it’s at all unreasonable to be somewhat skeptical toward the studies into relative importance of genes vs. various kinds of environmental factors.
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gazeboist said:
The confounder problems are what allows political bias to have a strong influence, perhaps (in both research areas, as the case may be).
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Charlie said:
The way I think about this is there are a lot of ways a parent can hinder a child’s genetic potential through an inadequate environment (don’t provide adequate nutrition, don’t read enough, don’t show affection, etc). But once you provide the US middle class parenting basics, there isn’t much more you can do to affect specific genetic traits.
I think height is a good example. Genetics determines how tall your child can grow. Nutrition determines if they can reach that genetic potential or if they will be stunted.
The same goes for intellegence, big personality traits, etc.
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Doyle said:
This isn’t true of height (and who knows– maybe not intelligence either). If you have a diet with an unhealthy amount of sugar as a child you are likely to grow taller than you would with a better diet with less sugar.
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Sophia Kovaleva said:
Actually, are the studies on long-term effects of childhood sleep deprivation? I can see how it can be bad not just at the time but also long after, but I wonder if it has been studied.
Also, here’s a weird one:
https://en.wikipedia.org/wiki/Biology_and_sexual_orientation#Twin_studies
No idea if the methodology is good enough, and if so, how to interpret this.
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Mircea said:
Maybe I don’t know enough about the research under discussion, but my first reaction to ‘what you do as parent doesn’t really matter for the final outcome of your kids’ is always ‘So what? It damn sure does for the intermediate outcome!’ I mean, technically speaking the final outcome for all kids is ‘dead and gone’ and it’s probably true (yet unfortunate) that I can’t prevent that outcome for my kid.
People have scoffed at my desire to teach my kid baby sign language for exactly that reason. ‘But kids who learn baby sign language don’t have a larger vocabulary when they’re 8, so why bother?’ Well, because it’s interesting to me as a parent (which makes me happy, which makes me a more engaged parent) and might make a difference in baby’s second year of life – better communication abilities are known to reduce frustration. No clue whether being less frustrated as a baby will directly result in better outcomes for HER, but it will result in happier, more relaxed parents. Since attachment theory and is definitely a thing, that sounds like a good deal. And parenting is stressful enough that parents’ happiness and reduced stress is valuable in itself.
(The result of the baby sign language experiment is, so far, that 11-month-old baby doesn’t give a damn about sign language but is also naturally low in frustration, so it’s a wash.)
My own parents made a bunch of mistakes (fighting dirty before, during and years after their divorce, making me their sole support person and responsible for their emotional stability) that definitely caused me a lot of damage I had to overcome. Maybe I’d still be prone to depression and an overly developed sense of responsibility if I’d grown up with parents who didn’t make those mistakes (and didn’t substitute them with equally bad things). But, you know, I’d probably have a better relationship with my parents and might be able to rely on them for support. Or ask them for advice. Which may not necessarily affect me or my child in the very long time, but might make today and the near future a bit more fun.
In short, I fully agree with you that while you can’t make a person happy, you can definitely make them miserable. And even if that doesn’t matter much in the long term, I can’t imagine it not mattering for that particular relationship. And short-term optimization is also worth something.
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Randy M said:
We did the sign language thing with our oldest. There weren’t a lot of signs we bothered to impart and fewer picked up, but having signs for “wet” and “more” and “milk” instead of grunts and cries was nice.
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Murphy said:
I think this post is sort of attacking a strawman version of the argument that parents seem to make a surprisingly small difference.
An important point is that if you’re measuring a sample then only the variation in your sample is being measured. Perhaps I’m putting it poorly.
Imagine a population living in a village who all have a weird genetic mutation that makes them into mathematical savants.
It’s entirely 100% genetic but everyone in the village carries the gene.
But.. if you sample only from people in the village (where the allele has achieved fixation with 100% of the population carrying it ) then it will look like all variation in mathematical ability is environmental.
To take an extreme case, a parent who takes their kids out back and shoots them in the head, killing them, is making parenting 100% of the relevant influence on their childrens life outcomes. (short as they are)
But that says very little about whether one of their kids had a set of alleles that would have carried one of them to Harvard and the other of them to become a serial killer.
But parents don’t often actually shoot their kids in the head so in any sane sample of the population you’re not gonna have many parents who did that… so the fact that a parent can theoretically have that close-to-100% control of their childrens life outcomes doesn’t really tell you much.
That 85% is telling you more about the normal variations in the sampled population. Lots of parents start out sure that they’re going to move heaven and earth to do everything for their child to make sure their kid will be the next Einstein… but the practicalities of life mean that most of them end up not succeeding quite as much as they would have liked and all that those good intention and how much of them materialize boils down to about 15% of real variation.
Countless parents decide they’re going to imitate the Polgár’s but you don’t hear about all the kids who ended up pretty unexceptional.
You absolutely can maim and traumatize your child or mainline thalidomide for the entire pregnancy…. Kids with no arms and legs or kids too emotionally screwed up to speak tend to have poor life outcomes… but since most parents *don’t* do that it’s not counted much in the analysis.
If you’re measuring the effects of something or other on peoples speed running 100 meters someone might choose to curl up and go to sleep at the starting line but since most people *don’t* other things like muscle mass will tend to look much more important if you sample real runners and their performance. If you point to the one guy who fell asleep at the starting line to try to claim it’s all about motivation then you’ll probably be mostly misleading.
You can poison and starve your kids… but most parents work like hell to keep the starvation and poisoning to a minimum. Across 300,000,000 people you can still find plenty of awful parents but if they’re only a handful out of the thousands in some sample for a study then they’re not going to show up as a significant part of the variation.
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ozymandias said:
I believe you’ve misread the study. It didn’t find 85% genetic and 15% shared environment. It found 85% genetic, 15% unshared environment, and 0% shared environment. So, in fact, how much parents fail at imitating the Polgars doesn’t result in 15% of variation, it results in 0% of variation– according to this study.
Perhaps you live in a better-run country than the United States, but in the United States there are quite a few cities in which the water is poisoned with lead. This is a very real effect of shared environment!
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FOOFy said:
I’m confused on how you got that conclusion from the study linked at the top of the article? The study found numbers for genetic and unshared environment by *assuming* no shared environment effects exist [0]. Shared environment wasn’t measured as zero, it was explicitly excluded from the calculations.
Is there a better study with similar results? The ones talked about in this paper have way more than 15% unshared environment.
[0] “Since previous research on genetic and environmental effects on NEO-PI-R domain scores (see Bouchard & Loehlin, 2001,for a review), and – more importantly – an inspection of the twin correlations do not indicate systematic effects of the environment shared by siblings, *we did not consider shared environmental effects in our models*. To the degree that assortative mating of twins’ parents, gene–environment interaction and gene–environment correlation affect the phenotypes observed in our study, parameter estimates will be distorted (see Neale &Maes, 2004, for more details).”
(also: hi! I’m new here.)
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Murphy said:
Sure, it’s a real effect but not a gigantic one. (though getting the quantified effect size is hard because apparently a lot of the studies are confounded all to hell by poorer people in poorer districts being more likely to have crappy water along with crappy everything else and controlling for x tends to be a crapshot. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1367853/)
If your kid ends up with 10 ug/Dl extra lead in their blood they might end up 3 IQ points lower than they would be otherwise. if you had 2 identical twin kids and one was 3 IQ points below the other how reliably do you think you could tell which was the one with lead in his blood and which without?
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jossedley said:
I’ve sort of vaguely followed Bryan Caplan’s arguments on parenting, and if I understand them correctly, it’s:
1) Some things are well known to cause damage to children. Don’t raise them in a horrible Romanian orphanage, abuse them, or feed them lead.
2) Everything else that yuppie parents do (enrolling them in select soccer, demanding that they continue with piano lessons, spending extra time reading to them) seems to be a rounding error when viewed against genetics, overall environment and background noise. Do things with them that you and they enjoy.
I’m not sure I agree, but it’s attractive to think so.
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