Bryan Caplan  

The Inelasticity of IQ

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Unlike referees for academic journals, the blogosphere produces a lot constructive and thought-provoking criticism. Check out Biopolitical and Tyler Cowen's responses to my recent post on IQ. Biopolitical immediately brought up an issue worth elaborating on:

I can see no difference between IQ and schooling as matters of policy.

1. We can change schooling. We can implement a successful policy of increasing schooling and, by doing so, achieve some economic benefits.
2. We can change IQ. We can implement a successful policy of increasing people's IQ and, by doing so, achieve some economic benefits.

But, someone can reply, IQ is heritable!

1. Yes, IQ may be heritable.
2. But years of schooling (or any other measure of schooling) may also be heritable.


1. We can change the mean and the variance of heritable traits.
2. We can even change the heritability of traits.

As a general rule, this is entirely correct. But not for IQ. The interesting thing about IQ isn't simply that it's highly heritable, but at least in rich countries it's been very difficult to find any environmental factor that can enduringly increase IQ. While many people uncomfortable with IQ research seek refuge in Dickens-Flynn, this is actually one of my main inspirations. We know lots of ways to temporarily raise IQ, but virtually nothing that permanently raises it. Even adoption at birth by a high-IQ family has zero apparent effect on adoptees' adult IQs.

Tyler Cowen brings up the Flynn effect, but he virtually answers his own objection:

Surely this deserves some discussion of the Flynn Effect, that near-universal albeit mysterious process whereby average IQs rise each generation. Should we re-gear government policy to subsidize whatever factors deserve the credit for this phenomenon?

If the Flynn effect is "mysterious" - and it is - it's going be to awfully hard to subsidize the factors that are responsible for it!

The bottom line is that the popular view that IQ can't be changed (as economists would say, that it's "perfectly inelastic") is literally false but roughly correct for most practical purposes. Better nutrition might help in poor countries, and if someone figured out the cause(s) of the Flynn effect we might be able to permanently make people a lot smarter in rich countries too. But that's about it.

Next post: Why Tyler underestimates the libertarian implications of IQ research.

Comments and Sharing

COMMENTS (20 to date)
Scott Scheule writes:

God, you're cool.

Laural writes:

Nothing that raises IQ? breastfeeding!

Patri Friedman writes:

I generally agree with you, however I would extend the "nutrition" argument to rich countries. First, the poor in the US have particularly bad diets and prenatal nutrition, which can affect IQ. And second, I think that almost everyone in the US has a diet deficient in omega-3 fatty acids. There is some evidence that prenatal supplementation w/ n-3 fatty acids increases IQ by several points, ie this study.

John S Bolton writes:

Maybe the heritability of IQ is bunched towards the fat middle of the curve, and such that environmental interventions have greatest effect at the top and bottom percentiles. In some countries, the majority are in conditions as bad or worse than the bottom few percentiles of the rich ones. It could be this way in a racial pattern, too, such that an intervention that is economical for the bottom percentiles of the white population, will do nothing much for the midlevels of the black distribution. If it were that way, a successful intervention could increase the gap that it was trying to reduce. Example: cochlear implants for infants.

Rob Sperry writes:

Post birth there are still several things which can at least raise the verbal component of IQ.

Baby Sign Language has longitudinal studies indicating IQ benefits on the order of 10 points.

Having the parents believe that the babies are taking in information about the world has good correlations.

The more you talk to the children the better their verbal development. Talk in a clear voice, don't babble. Elevated pitch is good. Make as much of your Talk positive as possible... if the only time you talk to them is to tell them "no" it will stunt development.

Focus on talking one to two grammatical stages ahead of the child. This starts with making pre-word sounds and goes on.

If you can do multi-lingual that has long term benefits though it will delay initial language capability.

Anyone else know of practices with good experimental data to back them up?


Zubon writes:

If we believe that IQ is heritable, which could explain some portion of the Flynn effect (the bottom of the intelligence distribution fails to reproduce due to death, incarceration, etc. more often than the top of the distribution fails to reproduce for the various reasons the highly educated have few children), then the most direct way of subsidizing it would be a sliding scale of subsidy/tax based on IQ. That is, pay some people to have children and fine others for it. Granted, most societies have rejected eugenics as a means of societal change, but economists have never stopped discussing things just because societies reject them.

(I have seen few discussions that remain civil after someone suggests that some people are congenitally advantaged over others, so I will just apologize now in case this heads south.)

Randy writes:

Question; Why do we assume that above average intelligence is "better"? Nature measures "better" in terms of survival. Who's numbers are increasing? - and who's declining?

As space is limited, I'm going to skip a few thoughts here, but follow if you can. What is the future of intelligence without aggression?

eric writes:

The Flynn effect is a challenge, but it is often misinterpreted. First, the rise has been across all groups in countries where it exists, so it isn't closing those annoying racial gaps. Secondly, it may have disappeared. See

Deb McAdams writes:

Is it not true that there have been IQ differences comparable to those in the US between groups such as Irish and English in England and between Korean and Japanese in Japan - while descendents of these groups in the United States do not show comparable IQ differences?

Sowell would say that the Flynn effect may be mysterious and unexplained, but it goes a way towards disqualifying a theory that IQ is purely genetic if IQ increases have been noted to increase where there has been no genetic change.

Roger McKinney writes:

If the purpose of education is to provide the basic skills necessary to get a job and participate in society at a minimal level, then government subsidies are worthwhile, because most poor children are born with sufficient IQ to learn to read, write and do basic math. Private charity could accomplish the same thing, but as early American reformers learned, private charity is too fickle to produce sustained improvements. Research shows great gains for early childhood and grade school educations for poor children.

However, beyond the basics, governmental expenditures appear to be a major waste of money. No correlation exists between the amount of money spent and standardized test scores in middle and high schools. Government subsidies of college education have driven up the cost of degrees while deflating their worth in the marketplace. Today, workers need bachelor degrees for jobs that used to require a high school diploma, even though the work is no more difficult. Most new jobs are in the trades and will be for a very long time. Finally, as McKinsey & Co. learned, the most important education takes place on the job, related to a specific task, and paid for by employers.

meep writes:

The fact that Koreans and Japanese in Japan should an IQ gap, and those of Korean and Japanese descent in America do not says nothing to the heritability of IQ.

Obvious reason: the population that stayed in Japan is not the same population that went to America. Those who emigrate are likely very different from those who stay put -- risk-takers of a certain sort, say. This may or may not have anything to do with IQ (for example, once you got to America, you had to do well enough to have children who had children, etc. Not all immigrants in America have thrived.)

There are genetic variations within any human group.


Again, stating something I've stated before, I'm not sure why we should be worrying about IQ here. The question is material results, in terms of productivity. You can have average IQ people who are highly productive, just as there are high IQ people of average productivity levels. I believe Roger McKinney is more on the point -- trying to change IQ is silly, but training people to be productive with what they've got is useful.

dsquared writes:

[at least in rich countries it's been very difficult to find any environmental factor that can enduringly increase IQ]

practising IQ tests?

John S Bolton writes:

The relevant consideration would seem to be the present and future governmental malleability of IQ, especially as between groups such as races, not the past flynn effects which had apparently zero narrowing effect on the relevant intergroup gaps. If this were not so, we wouldn't be scrambling to maintain affirmative action for the second and even third generation of eligibles in the US.

John S Bolton writes:

Regarding the point raised by meep; the fact that we can get productivity increases by matching low and high IQ for different occupations within some overall distribution, does not take away from the consideration that a higher average IQ, in the totality, allows for a much more productive overall mix of occupations. Once this is recognized, the malleability or elasticity again surges into paramount position.

Dog of Justice writes:

practising IQ tests?

A distinction should be made between IQ scores and underlying g. IQ scores are only useful because they are our best available way to estimate g; it is g that influences economic success. Practicing IQ tests could raise IQ scores but not affect g, so it would be a pointless exercise.

Next post: Why Tyler underestimates the libertarian implications of IQ research.

I'm definitely looking forward to this. I try to hold libertarian policy positions whenever it's sensible, but when it comes to IQ research I cannot stomach the pure libertarian position of letting the rich genetically enhance their children while the poor, unable to afford the technology, are left in the dust -- as a result I'm a "democratic transhumanist". There may be some crucial ideas that I'm missing, however.

Brian Horrigan writes:

You seem to be confusing two different, and each important, issues.

The first is the elasticity of IQ to any government interventions or programs. In industrial societies, that elasticity appears to be low.

The second is the elasticity of labor supply of individuals in various IQ ranges. That is very different. Government programs or policies may have a profound impact by discouraging employment, hindering occupational choice, limiting entrepreneurship, or forcing immigration.

I wonder if Hitler did not permanently reduce the average IQ in Germany, which is ironic in view of eugenics views. I wonder if Pol Pot did not permanently reduce the average IQ in Cambodia by killing all those in intellectual professions.

Claudia writes:

We know lots of ways to temporarily raise IQ, but virtually nothing that permanently raises it.

The obvious way is to prevent environmental exposures that reduce IQ, or cause mental retardation.

In addition to the factors mentioned above, remember the terrible IQ toll caused by fetal alcohol syndrome:

Mr. Econotarian writes:

My feeling is that the governmental and CULTURAL barriers to economic growth far outweigh any due to IQ heritability.

Certainly high IQ enables people to learn things faster, but a lot of high-IQ people believe in socialism, creationism, and other fantical things that take away from economic growth.

Roger McKinney writes:

This all reminds me of the old Dust Bowl joke in which so many Okies migrated to California that they raised the average IQ of both states!

Rick writes:

I don't see the challenge as how to raise IQs (setting aside dog's genetic engineering for now), I see it as how to increase wealth, in order to give more people the chance to fully express whatever genetic endowment they may have, including IQ.

Murray & Herrenstein's wonderful observation, for which they receive absolutely no mention, is that individual people prefer being who they are, and do not want to be someone else.

If this is difficult for you to understand, think about how many IQ points you would be willing to sacrifice to be slightly taller, a better musician, more coordinated, have a better sense of smell, etc. Then ask yourself why lower IQ people would be willing to be slightly shorter, worse musicians, less coordinated, or have a worse sense of smell, just to be like you.

They don't, of course.

When the world is wealthier, I can use my high IQ earning potential to buy tickets to see Shaquille O'Neal use his massive bulk to dominate a basketball court, earning millions of dollars in the process.

When the world is poorer, both Shaq and I are worse off, even if our IQs remain the same.

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