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COVID-19 Case Fatality Rate

Researchers are hard at work to determine all facets of COVID-19 (https://ourworldindata.org/coronavirus for example). I'm no expert, but I just wanted to play with some data a bit and see what I got. I do sort of thing a lot, and decided to share.

This is a quick attempt at estimating the COVID-19 mortality rate / case fatality rate (number of people who die from it over number of people who got it). That's not the only important number, and can vary from place to place given appropriate medical attention, etc. But I ran across this tweetNo photo description available.
and I was curious about what story that data might tell us.

Disclaimer up front. There's a lot we don't know as of this writing (March 16, 2020) about COVID-19. There may very well be people who have it without symptoms or who have otherwise not been tested. People who have it now may die from it. People who have it now may recover from it. There's a lot of uncertainty.

Also, disclaimer, I'm having a little trouble verifying those numbers in the tweet (also some of the percentages don't quite match the fatalities and cases listed in parentheses). But I'll run with them for now, as they seem at least close to values here: https://ourworldindata.org/coronavirus.

A simple model

Again, work is ongoing in this area by subject-matter experts (which I am not). But current case-fatality rate estimates seem to be somewhere between 0.25%-3.0% (https://wwwnc.cdc.gov/eid/article/26/6/20-0320_article#r7).

I wanted a simple model that assumes that the error in case-fatality rate is exponentially decaying. That's a simple way to model having an actual rate that things are slowly approaching. Again, lots of reasons that might not be true.

Using those values in the tweet, I got the following:
This simple model thus implies the case-fatality rate is something like 0.63%. That's well within the feasible values in the CDC research paper above. And in fact, after correcting the Diamond Princess cruise ship data for age (https://wwwnc.cdc.gov/eid/article/26/6/20-0320-t1) is exactly the case-fatality rate the researchers got in that paper.

Anyway, in lieu of some final profound insight, go wash your hands.

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