David Brooks and Malcolm Gladwell wrong about I.Q, Income and Wealth

In his book “The Social Animal”, reviewed here, David brooks writes:

“Once you get past some pretty obvious correlations (smart people make better mathematicians), there is a very loose relationship between IQ and life outcomes.”

Brooks further cites a study claiming that there is “no correlation between accumulating large wealth and high IQ.”

Both claims are wrong. The result Brooks cites is after “controlling” for education and income. But education and income are themselves functions of I.Q, so you shouldn’t control for them if the question you want to answer is how I.Q effects life outcomes.

I have not seen this graphed online, so let’s visualize the relationship between an estimate of I.Q and income and wealth so you can see for yourself. The source is NLYS79, a dataset which tracks a representative sample of the U.S population. Intelligence is approximated by the military when the individuals in the sample were mostly teenagers, while income and wealth data is for the same guys in their 40s. The sample is restricted to non-Hispanic white men.

For this group the lowest decile is people with I.Q below 84, and the highest decile above 116, which is not a very high cutoff. So keep in mind that we are not talking about only super-geniuses, in which case the results would be even stronger. Also remember that the middle of the distribution have very similar I.Q scores, the 5th decile is around 101-104, and the 6th decile around 104-108.

As you can see Americans men lucky enough to be born either with genes or a home environment that facilitates high I.Q earn more and accumulate more wealth.


The strong link between I.Q and earnings is well known by labor economists, but perhaps not by the affluent and high-I.Q readers of the New York Times. Obviously most of it goes through education. As technological development makes I.Q more valuable and unskilled labor less valuable, this disparity is increasing.

Another common claim of Brooks and of Malcolm Gladwell is that I.Q may matter, but only until around 130, after which it becomes meaningless. This is also wrong. Many previous samples have had too few observations to make reliable inference about the effect of I.Q above 130. Of course not having sufficient data hardly justifies Gladwell confidently claiming that I.Q above 130 is irrelevant even for scientists in technical fields (which I and others who are not smart enough to handle advanced mathematics could have told you from personal experience was a bizarre theory). After all, 130 is not that high, around the mean for a Harvard or SSE student.

This recent paper by Heckman, Gensowski and Savelyev studies the life outcomes of the Terman sample, which entirely consists of American men and women with I.Q above 135 (in some cases far above 135). They find that I.Q has a significant effects on earnings and educational outcomes, also for those above the 135 I.Q threshold. Another Malcolm Gladwell myth busted.


There are some policy implications from this realization. One is that smart and successful people shouldn’t congratulate themselves so much. They didn’t so much “earn” their talent than were lucky in the gene/environment lottery. If you are born healthy, with high I.Q genes and with educated parents and a good home environment you are expected to earn more than a more disadvantaged child who exerts the exact amount of effort through life.

Unlike libertarians, Conservatives believe that those who were the recipients of good fortunate have a moral obligations towards the rest of society, in particular to the people who do their best but just have less marketable skills.

Another is that the left is wrong about the market allocating income mainly based on chance, connections or “power”. In fact, earnings are strongly linked to intelligence, which indicates that they are linked to productivity, just as economic theory predicts. Poor people are on average less productive than rich people, a claim which may sound obvious (almost tautological) to an economist but which outrages a lot of people on the left.

Denying the link between productivity and earnings is very important for the modern left, as their entire source of outrage is based on the view that the capitalist system “exploits” the poor. More likely, because of the modern welfare state and because of the growing importance of human capital, more resources are transferred from the productive rich to the poor than vice-versa. There is so little demand in the labor market for unskilled people that the poor in industrialized countries increasingly don’t even work full time.

The fact that the rich don’t exploit the poor doesn’t mean the rich shouldn’t help the poor. But it’s one thing to claim you are rich because you are stealing from poor people, and another to believe you have an obligation to help all members of society due to randomly having being granted more valued skills. Fairness perceptions are not only a function of the type of distribution we desire, but to an even greater extent a function of the process we believe creates inequality.

I suppose David Brooks and Gladwell give an inaccurate impression about I.Q and income/wealth in order to make their readers feel warm and fuzzy. But that is not an accurate depiction of the world we live in, we live in a much harsher and more unfair reality.

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