It's no secret that ideology is one of the factors that influences which evidence people will accept. But it was a bit of a surprise that ideology could dominate decision-making in the face of a pandemic that has killed over a million people in the US. Yet a large number of studies have shown that stances on COVID vaccination and death rates, among other things, show a clear partisan divide.

And it's not just the general public having issues. We'd like to think people like doctors would carefully evaluate evidence before making treatment decisions, yet a correlation between voting patterns and ivermectin prescriptions suggests that they don't.

Of course, a correlation at that sort of population level leaves a lot of unanswered questions about what's going on. A study this week tries to fill in some of those blanks by performing controlled experiments with a set of MDs. The work clearly shows how ideology clouds professional judgments even when it comes to reading the results of a scientific study.

Call a doctor

The work primarily focuses on a panel of about 600 critical care physicians—the people who are most likely to be the first source of treatment for those who develop severe COVID-19. It also involved a panel of 900 people who aren't involved in medicine to provide a comparison population. While some initial surveys were done earlier, most of the data comes from the spring of 2022, long after COVID-19 vaccines had established their effectiveness in limiting severe symptoms of the disease. By then, a couple of widely hyped "cures"—hydroxychloroquine and ivermectin—had been definitively ruled out as therapeutic.

All the participants were asked to self-rate on a seven-point scale, from very liberal to very conservative. For most studies, the answers from the liberal and conservative participants were evaluated in terms of how greatly they differed from those of the moderate participants.

When asked about the effectiveness of treatments, the non-MDs showed exactly the sort of behavior you'd expect from politically polarized subjects. Liberal participants were more likely than moderates to say vaccines worked and less likely to ascribe effectiveness to ivermectin and hydroxychloroquine. Conservatives showed the converse behavior, being enthusiastic about ivermectin and hydroxychloroquine and less likely to think vaccines worked. If you plot these results across a liberal-to-conservative axis, the result is a nearly straight line with a slope that represents the liberal-conservative difference of opinion.

For physicians, things were considerably different. Here, the lines were largely straight and flat from very liberal to moderates, indicating that these physicians all had similar opinions on the value of these three medicines. But then the graph changed moving from moderates to the conservative end of the spectrum. This indicates that, among experts, the political polarization is one-sided. In other words, the opinions of liberal MDs look like those of moderate MDs, while the opinions of conservative MDs are difficult to distinguish from those of non-experts.