Inconvenient science

Will Flanders:

Wisconsin Governor Tony Evers instituted a statewide mask mandate on July 30. The mandate is likely unconstitutional, as the governor only has the power to declare an emergency declaration for 60 days for a particular crisis, and he already used that power in March.

But perhaps an even more important question is whether the mask mandate has had any impact on the spread of the virus that it is purported to help mitigate. With the benefit of time, we can now begin to answer that question.

According to the Centers for Disease Control and Prevention (CDC), COVID symptoms take 1-14 days to develop. We have surpassed the 14-day mark, and should be well into a period of secondary spread for anyone who has developed the virus since the mandate went into effect. But, to give the governor the benefit of the doubt, we will only look for the effect of the mandate starting a week after its implementation. This gives us 13 days of data after the mandate, which we will compare to 13 days before. The chart below shows the daily positive test rate in Wisconsin. The red line represents the point which we consider to be “post mandate (August 6).”

COVID Positivity Rates, July 24-August 18 (Wisconsin)

Visually, the mask mandate has had no effect. Indeed, average positivity rates for this period are actually slightly higher than for the period preceding the mandate (6.5% before compared to 7.3% after). But to be doubly sure of this, we also need to account for the number of tests that are being conducted. Additional testing tends to drive down positivity rates, meaning that, theoretically, there could be some impact of the mandate still if testing had substantially changed.

The table below uses regression analysis to simultaneously account for the mandate and the daily number of tests in the thousands. Accounting for daily tests, the mask mandate is actually significantly related to an increase in positive tests of about 1.7%. Daily tests has the expected relationship to positivity rates—more testing tends to lower them.

Does this mean that the mask mandate has had a negative impact on the state’s COVID rates? Likely not. But when the effect is in the wrong direction, we can be relatively certain that the mandate has not had the intended impact of mitigating the virus.

A similar pattern holds if we look at an area of the state that implemented a mandate earlier than the statewide mandate, Milwaukee. Below is the trend in cases in Milwaukee County, again using the same number of days before and after the mandate, plus a seven day buffer.

COVID Positivity Rates, June 27th-August 18th (Milwaukee County)

One caveat to this is that we are using county-level data while the mandate only affected the city. However, given that more than 62% of county residents live in the city, we ought to see some relationship here if one exists. There is a slight drop in positivity following the mandate, from about 11.2% to 10.2%. But this drop does not reach the level of statistical significance.

All of this is not to say that wearing masks is the wrong thing to do. Citizens ought to have the common decency to respect the wishes of others, and to follow the rules of businesses on private property. There is scientific evidence that the proper wearing of a mask can reduce the risk of transmission.

But the incremental impact of mandates remains an open question. Indeed, it appears that many Wisconsinites wear masks on their own, without government interference. The bottom line is that Evers’ mandate, in addition to being unconstitutional, is ineffectual.

The argument can actually be made that, contrary to what Evers and his apologists want you to believe, that nothing the state has done, including the Safer at Home orders, has slowed the spread of the coronavirus. (And the evidence of mask-wearing reducing the spread is not persuasive.) “Flattening the curve” has, as predicted, made the pandemic last longer, which means it may have infected, and be infecting, more people than otherwise would have happened.

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