Nov 23, 2021 - COVID

Experts: Polk County's school masking data is messy

Illustration of an apple wearing a covid mask.

Illustration: Brendan Lynch/Axios

The Polk County Health Department's review of COVID-19 data shows that transmission rates in county schools decreased soon after a Sept. 13 federal court ruling paused Iowa's ban on school mask mandates.

  • County health officials told Axios that school transmission rates have fallen faster than the overall community's case decline.

Yes, but: While larger studies suggest masking is a likely contributor to the decline, two Iowa university experts say it's not so simple.

Why it matters: You'll probably be hearing more about the effectiveness of the mandates in coming weeks.

What they're saying: Iowa State University economist Dave Swenson and Maryann Huey, Drake University's Mathematics Department chairperson, are warning that the county can't conclusively show that masking is driving the drop in cases.

  • County health officials are comparing two different measurements: school transmission rates and countywide case counts.
  • Swenson and Huey say that's not a reliable way to compare the data because the county doesn't collect the two the same way.

Plus: There are too many factors to draw a definitive conclusion, they said.

  • For example, school data is often incomplete because it relies on parents to test their children and report their results, Huey said.
  • Also, are less likely to develop severe illness or die from COVID-19 and may never know they are infected, according to the CDC.

The other side: Meg Schaeffer, an epidemiologist working as a consultant for Polk County, said it's important to recognize that they're not comparing the "actual rates of Polk County residents to students/staff in schools."

  • Rather, the county is "displaying the trend of each for the sake of comparison as staff/students are a subset of residents."

Between the lines: The health department attempted to standardize the comparisons but it still leaves an assumption that schools are trending within the confines of the overall population, Swenson told Axios after reviewing Schaeffer's written explanations about the data.

  • The county's graph, shown below, would likely be misread or misunderstood by a casual reader, he said.
A chart showing COVID-19 transmission rates in schools.
The orange line on this chart published by Polk County's health department shows COVID-19 transmission trends in Polk schools measured against community trends. Graph courtesy of the Polk County Department of Health

Get more local stories in your inbox with Axios Des Moines.


Support local journalism by becoming a member.

Learn more

More Des Moines stories

No stories could be found

Des Moinespostcard

Get a free daily digest of the most important news in your backyard with Axios Des Moines.


Support local journalism by becoming a member.

Learn more