Several critics of the study claimed it is yet another example of the classic problem of confusing correlation with causation. “The first problem is that they seem to be making the big mistake of assuming that correlation equals causation,” says Jermaine Jones, a Columbia University neurobiologist whose study found naloxone didn’t increase heroin use. “This misinterpretation of data is one of the first things we are taught in psychology.” Jones went on to tell me about the classic example of ice-cream sales and murder rates. Of course, the sugar high doesn’t spark killing rampages; the hidden variable there is summertime.

But Doleac and other economists say this is one of the differences between public-health research and economics. Economists often make “causal inferences”: They study natural experiments like law changes, use statistical tools to rule out other explanations, and draw conclusions about cause and effect. (Doleac, in turn, criticized the methods used in the studies that came to different conclusions than her own.)

“Public-health people believe things that are not randomized are correlative,” says Craig Garthwaite, a health economist at Northwestern University. “But [economists] have developed tools to make causal claims from nonrandomized data.”

This difference of opinion about causality led to exchanges like this one, between one of Doleac’s critics and another female economist, Analisa Packham:

The other thing critics brought up is that Doleac and Mukherjee’s article is not yet peer reviewed—they plan to submit it to journals soon. But this, too, is an important difference between economics and some other types of health research. Economists tend to put out working papers and circulate them among colleagues long before they submit to journals. For example, Doleac and Mukherjee’s paper thanks several economic conferences and their participants in its acknowledgments. These colleagues—sometimes in pressure-cooker-esque seminars—ask questions and make suggestions, after which the paper is revised, then submitted.

Though this is not quite the same as a journal’s peer-review process, it’s not quite a personal Word document uploaded to the internet, either. Because of that, economics working papers are regularly discussed by journalists, academics, and even policymakers before they’re formally published in a journal.

What’s more, the Twitter conversation at times turned unusually venomous and condescending, especially for an economics paper.

In some cases, it seemed more suited to, say, debates about putting peas in guacamole or the potential outcomes of single-payer health care. The tone “felt sort of accusatory and ‘let me explain to you simple authors about how this works,’” Garthwaite says.

One person, for example, called Doleac “a ghoul:”

You are a ghoul who explicitly and in a published paper said saving people’s lives is a downside, the Brookings Institute should be razed and the earth salted — pacific palisades fan acct (@AlexCercone) March 8, 2018

Another implied that Doleac hates poor people. (It’s worth noting, of course, that opioid addicts aren’t always poor.)

just say you hate poor people it’s a thousand times easier than arguing against basic safety measures — Goth Ms. Frizzle (@spookperson) March 7, 2018

It led some to wonder how much of the pushback was about peoples’ interest in the opioid epidemic and how much was simply what happens when female researchers’ findings don’t quite toe the party line.

Paper idea: write 50 page causal inference paper and randomly assign female/male econs to tweet about it and estimate impact of gender on “correlation!=causation” responses. @jenniferdoleac — Jonathan Eyer (@jonathaneyer) March 9, 2018

All of this isn’t to say that Doleac and Mukherjee’s findings are the last word on the matter, or that they shouldn’t be scrutinized and (respectfully) questioned. They might still hit snags in peer review, or another study might come along and refute their findings. Such is the nature of science.