Friday , September 17 2021

Masks redux

Summary:
My previous post on Delta policy and masks led to some discussion that went off the rails, on twitter especially. An effort to summarize the point: From the literature I have read, masks can be moderately medically effective. The literature has pretty wide ranging estimates, from some studies and meta-studies saying no effect, and others saying ...

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My previous post on Delta policy and masks led to some discussion that went off the rails, on twitter especially. An effort to summarize the point: 

From the literature I have read, masks can be moderately medically effective. The literature has pretty wide ranging estimates, from some studies and meta-studies saying no effect, and others saying substantial effects.  

Delta has a reproduction rate of 6. (Again, best guesses with varying estimates.) Even if masks are 50% effective -- which is wildly optimistic -- they reduce the reproduction rate to 3. That's more than the alpha covid with no masks. Each person who gets it passes it on to three people, about every two weeks. 

If one wishes to stop the virus, only one goal matters: Getting the reproduction rate below one. e to the 3 t is not a lot less exponential growth than e to the 6 t.  (With t in two-week or so intervals.) 

Thus a public policy response that focuses exclusively on fine-tuning mask mandates, depending on the current level of infection is bound to fail its stated goal. That is the point. 

If our policy makers were willing to say "we are passing the mask mandate so it rips through the population a little bit slower" I might not be so grumpy. 

I am glad to see vaccine incentives finally percolating out, too slowly and late. I don't know that vaccines bring R0 below one, but they're darn close. 

You beat exponential growth when case levels are low, not by waiting until there is a crush.  


John H. Cochrane
In real life I'm a Senior Fellow of the Hoover Institution at Stanford. I was formerly a professor at the University of Chicago Booth School of Business. I'm also an adjunct scholar of the Cato Institute. I'm not really grumpy by the way!

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