Bryan Caplan  

Do Parents Affect How Long You Live?

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Parents - especially moms - spend a lot of time nagging their kids to eat right, get some fresh air and exercise, not smoke, etc.  If nagging changed behavior, and there is some validity to popular perceptions about "what's healthy," then parenting should affect life expectancy.  Does it?

According to the literature I've tracked down, the answer is no.  When you analyze life expectancy and mortality using twin studies, you get the standard behavioral genetic answer: genes aren't everything, but parents still don't matter.  A couple of relevant studies:

"The Heritability of Human Longevity," (Human Genetics 1996) looks at about 3000 Danish twin pairs.  It gets a heritability estimate for life expectancy of about 25%, with non-shared environment getting the remaining 75%.

"Half of the Variation in Susceptibility to Mortality is Genetic" (Behavior Genetics 1999) looks at about 9000 Swedish twins.  It gets a heritability estimate for mortality of about 50%, with non-shared environment getting the rest.

And here's a readable survey piece published in Nature in 2006.

At least in my experience, most parents claim that their nagging has long-run health benefits.  "It may seem OK to eat ding dongs and play videogames all day when you're ten, but you're building bad health habits that will haunt you later in life."  Once again, though, it looks like parents overestimate their influence.  If the short-run benefits of health nagging aren't enough to justify it, it turns out that you might as well just hold your tongue.


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COMMENTS (13 to date)
Gary writes:

Bryan, I'm mostly on board with Judith Harris's hypothesis, but one thing bothers me: why do parents believe so strongly that they can influence their children? Perhaps parents' intense efforts at influencing their children has some informational value about the parental profitability of such behavior. Have you addressed this in another post?

Fenn writes:

Reading the Harris book right now.

Muffin in oven w/ the timer set for July.

Glad I'm not having my first kiddo until almost 40, when I'm sanguine enough that my primary goal will be to help her be whoever the hell she is.

Caliban Darklock writes:

"It is a great failure to reason that because one can only do very little, it is as well for one to do nothing at all." - Glenn Harmaning, 2002

As a parent, I am perfectly aware that some 99% of what I tell my children is going to be ignored. But I keep telling them things, because that 1% is important. I don't know which 1% it is. I have no control over that. This is the price of dealing with other human beings; they're not machines, they don't always act rationally, and there's no magic "pay attention" button conveniently mounted on their foreheads.

I think of it this way: what I say doesn't direct behavior, it simply directs attention. If I give my children good rational advice, then good rational thought about the question will lead to better decisions on it. Directing their attention to it - repeatedly - will get them to think about the question, and I hope it will be good rational thought that leads them to answer the question well. Even if it's not the answer that I provided, or that I would prefer, a good rational decision is almost always better than a random one. If my own reasoning is sound, the good rational decision they reach is statistically likely to be compatible with my own recommendations.

caveat bettor writes:

I guess nagging parents hoping to avoid the shame of the Confucian academic work ethic is overdone in those Asian SAT scores, and its a genetic superiority?

Les writes:

I think that Caliban has it right. As a parent I believe that my duty is to give my children the very best upbringing that I can. So even if they will not follow my advice, at least they have had the guidance I owe them, and also they know where I stand.

From my own youthful follies I certainly know that I ignored my parents' advice many times. But youth can be impetuous, and ignore wisdom. So when I erred, I knew it and respected my parents for trying to do their best to guide me.

If they had simply ignored their responsibilities and merely said "whatever" I would have found it much harder to respect them.

Its not easy being a parent, and its not easy to take direction, especially when one is young. But doing the right thing is not always easy.

Arare Litus writes:

"why do parents believe so strongly that they can influence their children?"

They can, in the short run - one can argue that this is the only thing that matters, as once children are old enough they have enough collected evidence from life to make decent decisions themselves. Failures in those decisions will be based on human biases and other known effects; but this simply indications that we are not limited sharply by our childhood (I think that Harris does not look at the extreme cases of horrid abuse etc, where we would expect to see limitation). And as parents see the effect of their short term change in behaviour it makes sense for them to continue - evidence based action (plus, people like to nag).

Don't confuse long run evidence of lack of effect, this can be taken to merely mean that humans can learn/develop to make informed decisions themselves eventually, and that the evidence they collect in their lives are influential in how they behave. This seems like a very, very positive thing, and this should mirror any self reflection of your own life.

To me, I am unsurprised by the findings, though I am quite surprised and heartened by the *magnitude* of them. Without further evidence I take this to mean that people learn a lot from life and evidence they collect while living - considering how far humans have come this fits with what we see all around us, our own personal histories, and stories of people we know.

Overall, and I have to read more on this, my previous positive view of people & parents roles are strengthened by Harris' & others evidence. Short run modification: good, this is what parents are for - helping you get started. Long run "self actualization" and diminishing of our initial circumstances in life: good.

I don't think Harris presents her work in this light, but this seems the obvious and quite positive suggestion of her, and others, work. This is likely a marketing position in part - after all saying "parents don't matter" is more of a hook than saying "parents matter deeply in the short run, when they are parenting, and people grow into independent adults - just like people have *always thought* and all personal and historical evidence seems to suggest, I simply look to the literature and collect detailed measures of this and present them! Buy the book now!! ...No?" ... "um, Parents don't matter! Compelling evidence that is *totally* different than what people have always thought! Read - discuss - argue!!!"

Neal W. writes:

Are you talking about parents nagging their children who are adults? If you are talking about children when they are little I don't see how parents don't have an influence on their health. Who buys the food that's available to them in the house? Who cooks their food? Fat kids are the fault of parent.

JP writes:

I don't understand how studies finding that non-shared environment accounts for 50-75% of longevity tend to disprove that nagging has a positive effect.

ajb writes:

The point about Asian test scores is spot on. If it's just peers and external environment then the Asian kids should perform the same as their non-Asian classmates correcting for IQ, etc. But the average score differences (especially in Math) are far too large to be explained by any measurable difference in average IQ's. I think existing studies have differences in IQ swamping differences between siblings. But looking at group differences reveals how unlikely it is that parenting or broadly culture doesn't matter.

Even the adoption studies aren't clearcut. How likely is it that traditional, Asian families are going to adopt kids of a different race? Without that test sample, it's hard to see how to figure out the effects of parental nagging, Asian pro-study culture, etc.

So unless Bryan thinks much higher test scores don't correlate with long run performance in school or incomes I'm willing to accept this "small" effect as worth the effort.

Steve Roth writes:

Supporting Harris's argument that peers are what matter, a couple of studies cited yesterday in the NYT suggest that those with more friends live longer.

http://www.nytimes.com/2009/04/21/health/21well.html?_r=1&ref=health

Post hoc, of course...

aez writes:

It's late, so I'll say what I think outright...mmmmm, Swedish twins!

ericyu3 writes:

There was a study of Finnish (?) children (I can't remember where it is) that found that children born to younger mothers were more likely to live to age 100 (I think the effect was statistically significant). The likelihood of living to that age only has a small effect on life expectancy because so few people get that old, but twin studies would erroneously say that the effect is caused by genes (because twins are born at the same time), while it is actually caused by the decisions of the parents.

Nils writes:

I think it safe to say that parents can have a detrimental effect on the life expectancy of children. This includes everything from active (hurting, killing) to passive (not giving food, medicine). Caring parents will naturally try to do avoid doing bad things. From there, it is but a short step to actively try doing good things.

I understand Bryan's argument to be one-sided: only try to avoid hurting your children. The rest doesn't matter.

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