Proving once again that effort is not always correlated with income, I present this critique of a Justin Wolfers blog post…

A lot of people have written reviews of Piketty. The first few pages of a Google search revealed all these (I added Heather Boushey, who wrote a good one)*:

I believe that is diversity, because every human being is different.

Anyway, where to begin? Justin Wolfers wrote a little post, not a review, but it caught my attention. The headline of was, “Piketty’s Book on Wealth and Inequality Is More Popular in Richer States.” Distractable, that’s where I began.

Wolfers’ culminating line, “Vive la révolution!”, suited Scott Winship, who looked over Wolfer’s figures before sniping, “the buzz around the book has come mostly from rich liberal states along the Boston-to-Washington corridor.” But I think they’re both misinterpreting.

According to the Google search data Wolfers used, these were the top 10 states for “piketty” searches (Washington, D.C. excluded): Massachusetts, New York, Connecticut, Maryland, New Jersey, Illinois, Pennsylvania, Wisconsin, Oregon, California.

It looks to me that it’s actually education driving the search data. And that is a big difference. Let me explain.

Do data?

Microsoft Word tells me that the reading grade level of the publisher’s excerpt is 16.3, so it takes a 16th-grade education to read it. (Note that the “Boston-to-Washington corridor,” which was supposed to sound like a small sliver of the country, has 26% of the country’s college graduates.) So consider income versus college completion, which we can now take as a proxy for being able to read Piketty.

Wolfers writes, “I can’t tell you where Piketty has been least popular, because below a certain level of search activity, Google doesn’t release the actual numbers.” So he proceeds to leave 24 states out of his analysis (this will become important). Using per-capita income (converted to z-scores), and dropping 24 states plus the ridiculous outlier of DC, this is Wolfers’ income result (my calculations; he just showed scatter plots):

OK, leaving out the bottom half of the Piketty distribution, there is a strong positive relationship between per capita income and Piketty Google searches. Congratulations, you can have three jobs as an economist!

I kid Wolfers. But, come on! I don’t know what kind of data operation they’re running over there at the Upshot, but I would expect Wolfers to take it up a notch. First, control for college completion (percent of folks ages 25+ with a BA or more, also z-scored). See how it shows… oops:

The income effect is reduced but the education effect isn’t significant. (See how I showed you that instead of just going right to the results that support my argument?)

But go back to Wolfers leaving out the bottom half of the Piketty distribution. What’s wrong with that? I’m sure there’s some statistical way of explaining that, but just eyeballing it you’d have to say dropping those cases could cause trouble. The censored cases all have values of -.64 on the search variable. The relationship with income is weaker when the censored cases are included (shown in the red line) versus when he limits it to the top half of Piketty states (blue line):

What to do about this? An easy thing is just to include the censored cases at their values of -.64, just pretending -.64 is a legitimate value. That gives:

Now the income effect is reduced about three-quarters, and the college completion effect is three-times as large (with a t-stats to match).

But that’s not the best way to handle this. If only economists had invented a way of modeling data with censored dependent variables! Just kidding: there’s Tobin’s Tobit. This kind of model says, I see your censored dependent variable, and I crash it through the bottom of the distribution as a function of its linear relationship to your independent variables. So instead of all being -.64, it lets the censored cases be as low as they want to be, with values predicted by income and college completion. Sort of. Anyway, here’s that result:

Now income is crushed, reduced to literal insignificance. What matters is the percentage of the population that has completed college. It’s not that rich people like Piketty, it’s that college graduates do. Maybe because that’s who can read it. (I don’t know, I haven’t tried.)

What do economists read?

Of course, mine and Wolfers’ are both pretty crude analyses. There are only two reasons his was published on a major news site and mine was buried over here on an obscure sociology blog: (a) he writes for a major news site, and (b) his weak analysis lends itself to an emerging snarky narrative in which rich leftists are seen to whine about inequality but real people can’t be bothered (the main point of Winship’s review) — just reinforcing the echo-chamber model of knowledge consumption that people who are into “data-driven” news like to appear to have risen above.

For a real explanation, Wolfers (and Winship) need look no further than the rest of the Google Correlate results page to see the obvious fact that searches for Piketty are simply correlated with interest in economics. Here’s the search that is most highly correlated with searches for “piketty” across U.S. states: “world bank gdp” (r=.98):

Here are some other searches correlated with “piketty” at .94 or higher:

economic consulting firms

eu data protection

exchange rate data

gdp by sector

inflation target

journal of labor economics

london school economics

nber working paper

oecd statistics

oxford economics

panel data stata

stock market capitalization

the economist intelligence unit

us current account deficit

world bank statistics

Well, there goes your rich, liberal, “American left” theory of who’s driving the Piketty phenomenon. It might be true, but it’s not confirmed by the Google search data. My hot new theory: college educated people who are also interested in economics are disproportionately interested in Piketty.

* The reviewer pool: Mervyn King (The Telegraph), Paul Krugman (New York Review of Books), Tyler Cowen (Foreign Affairs), James K. Galbraith (Dissent), Daniel Schuchman (Wall Street Journal), Justin Fox (Harvard Business Review), Michael Tanner (National Review), John Cassidy (New Yorker), Martin Wolf (Financial Times), Jordan Weissmann (Slate), Steven Pearlstein (Washington Post), Scott Winship (National Review), Heather Boushey (Challenge)