A few of you may have read this recent New York TImes op-ed (hat tip Suresh Naidu) by economist Raj Chetty entitled “Yes, Economics is a Science.” In it he defends the scienciness of economics by comparing it to the field of epidemiology. Let’s focus on these three sentences in his essay, which for me are his key points:

I’m troubled by the sense among skeptics that disagreements about the answers to certain questions suggest that economics is a confused discipline, a fake science whose findings cannot be a useful basis for making policy decisions. That view is unfair and uninformed. It makes demands on economics that are not made of other empirical disciplines, like medicine, and it ignores an emerging body of work, building on the scientific approach of last week’s winners, that is transforming economics into a field firmly grounded in fact.

Chetty is conflating two issues in his first sentence. The first is whether economics can be approached as a science, and the second is whether, if you are an honest scientist, you push as hard as you can to implement your “results” as public policy. Because that second issue is politics, not science, and that’s where people like myself get really pissed at economists, when they treat their estimates as facts with no uncertainty.

In other words, I’d have no problem with economists if they behaved like the people in the following completely made-up story based on the infamous Reinhart-Rogoff paper with the infamous excel mistake.

Two guys tried to figure what public policy causes GDP growth by using historical data. They collected their data and did some analysis, and they later released both the spreadsheet and the data by posting them on their Harvard webpages. They also ran the numbers a few times with slightly different countries and slightly different weighting schemes and explained in their write-up that got different answers depending on the initial conditions, so therefore they couldn’t conclude much at all, because the error bars are just so big. Oh well.

You see how that works? It’s called science, and it’s not what economists are known to do. It’s what we all wish they’d do though. Instead we have economists who basically get paid to write papers pushing for certain policies.

Next, let’s talk about Chetty’s comparison of economics with medicine. It’s kind of amazing that he’d do this considering how discredited epidemiology is at this point, and how truly unscientific it’s been found to be, for essentially exactly the same reasons as above – initial conditions, even just changing which standard database you use for your tests, switch the sign of most of the results in medicine. I wrote this up here based on a lecture by David Madigan, but there’s also a chapter in my new book with Rachel Schutt based on this issue.

To briefly summarize, Madigan and his colleagues reproduce a bunch of epidemiological studies and come out with incredible depressing “sensitivity” results. Namely, that the majority of “statistically significant findings” change sign depending on seemingly trivial initial condition changes that the authors of the original studies often didn’t even explain.

So in other words, Chetty defends economics as “just as much science” as epidemiology, which I would claim is in the category “not at all a science.” In the end I guess I’d have to agree with him, but not in a good way.

Finally, let’s be clear: it’s a good thing that economists are striving to be scientists, when they are. And it’s of course a lot easier to do science in microeconomic settings where the data is plentiful than it is to answer big, macro-economic questions where we only have a few examples.

Even so, it’s still a good thing that economists are asking the hard questions, even when they can’t answer them, like what causes recessions and what determines growth. It’s just crucial to remember that actual scientists are skeptical, even of their own work, and don’t pretend to have error bars small enough to make high-impact policy decisions based on their fragile results.