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See the latest news and updates about COVID-19 and its impact on the Charlotte region, the Carolinas and beyond.

Fact Check: There's A Correlation Between NC Mask Order And Virus Cases Stabilizing

N.C. Department of Public Safety

The number of North Carolina's new coronavirus cases is beginning to stabilize. Two weeks ago, state Health and Human Services Secretary Mandy Cohen said there's evidence the statewide mask requirement is behind that.

"Our actions to slow the spread of this virus are having an impact," Cohen said. "Specifically, we see a direct correlation to the start of the statewide mask requirement at the end of June."

WRAL's Paul Specht joins us to assess Cohen's claim.

Lisa Worf: Good morning, Paul.

Paul Specht: Good morning.

Worf: So, what evidence did Cohen give that the mask requirement is keeping new coronavirus cases in check?

Specht: Now, we have to be careful here because she said "direct correlation," and what I learned from this research is that correlation does not mean causation. And so what she pointed to was the date that the mask mandate went into effect, which was June 26. And then she pointed to three weeks after that -- what happened to North Carolina's caseload three weeks after that.

And we looked at the three-week mark because it takes that long to see something go into effect. If people were not wearing masks before the mandate, it's possible that they got sick but didn't realize it until after the mandate was in place, so it's not really fair to judge the mask law until about three weeks after that.

Worf: And when we talk about new case numbers stabilizing, what does that look like here in North Carolina?

Specht: The best way to judge whether or not the numbers are stabilizing is by looking at the seven-day average, also called the rolling seven-day average, because it's updated every day. If you look at coronavirus cases every day, it's likely you'll see a variety. You know, you'll see it go up one day and down one day and up one day and down one day.

And so if you look at the average, the rolling seven-day average, it gives you an idea of what the trends are. And between late June and mid-July, we were going up and up and up to the point where in mid-July we were close to 2,500 cases.

Worf: New cases a day based on the rolling weekly average, then?

Specht: That's right.

Worf: And where are we now?

Specht: So, we looked at that. That was about three weeks after the mask mandate, and after we hit sort of that peak around July 18, we started to level off. We went back down to about 2,000 new cases, and then we went below that, and we haven't been at 2,000 new cases since then. And so, there is something to be said for that mask mandate. One could argue that since that went into effect in full, that it has played a role, although experts did say other things could be playing a role, too.

Worf: And who are the experts you spoke with?

Specht: We spoke with experts at UNC, Barry Bloom at Harvard University, as well as a doctor at University of Toronto and other places as well.

Worf: Did they say there is indeed a link between the drop in new case numbers and the mask requirement?

Specht: They said that it's fair to say there may be a correlation, but they say there are multiple other factors that could be affecting those smaller coronavirus caseload numbers. There could be local factors whether or not, you know, individual counties imposed new laws about, you know, going out to restaurants and things like that. Maybe people are traveling less.

Maybe the numbers started to go back down in mid-July because July 4 played a role and had boosted them because people gathered. So there are all these things to take into consideration. But here's the problem. It takes a long time to study all these different factors and tease out what the biggest contributing factor was. And that's what experts told us, is it's fair to say the law and the decline in coronavirus case numbers could be related. They would not go so far to say that it's provable at this point.

Worf: And so how did you end up grading Cohen's statement?

Specht: We rated this mostly true, and that's because, I know we've talked a lot about how you can't prove that one thing affected the other, but she didn't say that. She didn't say X caused Y. She said there's a correlation, which essentially means this thing happened, and then this thing happened, and they might be related. And that is true.

These Fact Checks are a collaboration between PolitiFact and WRAL. You can hear them Wednesdays on WFAE's Morning Edition.

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Lisa Worf traded the Midwest for Charlotte in 2006 to take a job at WFAE. She worked with public TV in Detroit and taught English in Austria before making her way to radio. Lisa graduated from University of Chicago with a bachelor’s degree in English.