One of the more frustrating aspects of the coronavirus pandemic has been the amount of disinformation swirling about. Much of this is politically motivated, perhaps unsurprising with the attention given to President Donald Trump's rambling, error-strewn press conferences. It may seem like commonsense that actively misleading the public during a national emergency has consequences, but now Fox News' two most-watched hosts have unwittingly performed a rather elegant experiment on their viewers that allows us to quantify that effect. The results are stark: greater exposure to Sean Hannity versus Tucker Carlson shows a measurable increase in the number of COVID-19 cases and deaths throughout March and early April.

Hannity and Carlson are Fox News' two biggest stars, each commanding around 4 million viewers for their respective evening shows (Hannity and Tucker Carlson Tonight). While often it can be hard to see daylight between their ideological pronouncements on-air, in early 2020, the two had markedly different lines on the coronavirus outbreak. Carlson began regularly covering the virus in January. During February, he did so with a growing sense of alarm that the United States could experience a heavy death toll—the same month that saw much inaction on the part of the federal government.

By contrast, Hannity gave the virus almost no attention in February. And when he began to discuss the virus at the same frequency as Carlson during the first two weeks of March, it was to minimize the threat compared to the number of annual deaths attributable to car crashes, shootings, or seasonal influenza. Additionally, Hannity also accused the Democratic Party of exaggerating the threat as a way of attacking the president. However, by mid-March, Hannity changed his tune once President Trump declared COVID-19 a national emergency.

The study comes from a group of researchers led by the University of Chicago's Leonardo Bursztyn and uses survey data gathered in April from 1,045 regular viewers of Fox News (aged 55 and over) to examine the timing of behavioral changes in response to the virus—when people began to cancel travel, isolate, increase the frequency of hand-washing, and so on.

The results are striking. Survey participants who preferred watching Carlson began changing their behavior on average three days earlier than other Fox News viewers. Meanwhile, participants who preferred Hannity acted much later—five days after other Fox News viewers, and eight days after Carlson viewers.

Next, the authors examined the data at a more granular level to determine whether there were local differences in the rate of COVID-19 infections or deaths in areas that watched more Hannity versus Carlson. They found that:

[C]ontrolling for a rich set of county-level demographics (including the local market share of Fox News), greater local viewership of Hannity relative to Tucker Carlson Tonight is associated with a greater number of COVID-19 cases starting in early March and a greater number of deaths resulting from COVID-19 starting in mid-March. In a set of permutation tests across socio-economic, demographic, political, and health-related covariates, as well as across geographical fixed effects to account for unobservable factors, we show that the established relationship is highly robust. Indeed, the estimated effects of exposure become stronger as we control for more factors.

The study then goes on to tease out whether there could be another reason for this correlation. For instance, could local sunset times affect the data? (Or, as the paper explains, "if people like to turn on their TVs to watch something when Hannity happens to be on instead of Tucker Carlson Tonight, the likelihood that viewers are shifted to watch Hannity is disproportionately large in areas where Fox News is popular in general.") But the effect remains. As viewership of Hannity increases compared to Carlson, there's a significant increase in COVID-19 cases in mid-March, which begins to decline later in the month as the two hosts' messages on coronavirus converge.

By this point, it's a safe assumption that some of you are screaming at your screens that the authors are idiots, because correlation isn't causation. But the study is well-controlled for other variables—for example, how rural an area is, how far it is from Seattle, or differential rates of health insurance—that could affect the local spread of COVID-19. For example, geography or rates of health insurance or educational attainment at the county level could explain these results. On top of that, the study builds on previous (recent) work that has shown that there are partisan differences in how people respond to emergencies—areas that saw more votes for Trump have lower hurricane-evacuation rates, for example, as well as GPS data that shows less social distancing in areas that watch greater amounts of Fox News.

Whether Fox News planned to conduct this experiment or not, it does elegantly show that dis- or misinformation during a public health emergency costs lives.