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Daily COVID model update for Monday, April 20

National growth rate 4.0% – possible peak in Massachusetts

Pretty good news again today. The national growth rate stayed at 4.0%, which is the lowest point we’ve seen to date. We usually see a drop in reporting on Sundays, but not this week. We saw the 2nd highest reported test day, with over 175,000 test results reported, so that gives me confidence that Sunday was not an aberration.

I refit my Logistic model on Saturday afternoon, and I’ve received several questions about what that means. Early on, I chose a functional form that is the one most often used for modeling disease propagation. I have recalibrated the model twice now to historical data, but haven’t changed the model form, which looks like this:

A picture containing text, whiteboard, bird, flying

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If that’s TMI, I apologize. In any event, models remain effective by learning from changes in the data over time. There are many reasons to recalibrate models, but in this case we’ve seen a lot of moving parts. Specifically, the rapid change in scope of testing, constantly changing definition of what a “reported case” is, and some historical reclassification of data. So we’ll use this model so long as it reasonably tracks actual reported data from day to day, and when something changes where the model is no longer useful, I’ll recalibrate it again. It looks like IHME revises their model about every three days. I’ll likely let mine ride much longer than that. Before active cases peaked, I used the model primarily to forecast peak cases, and it was quite close. Now I’m using the model to project when we’ll see active cases significantly decline.

As always, if you have any questions about my assumptions, or how I’m modeling, or want to know about Logistic modeling generally, drop me a line.

  • Likely date of active case peak (Chalke modeling): April 10
  • Likely date of peak deaths (IHME): April 15 (last revision on April 17)
  • Short term projection for tonight: 800,000
  • Total Test Results reported yesterday: 175,382
  • Total Pending tests reported yesterday: 11,324
  • National reported case Growth Rate yesterday: 4.0% (low point to date)

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