Always Check the Math

I just learned something new about COVID1-9, and it reminds me of my mantra to “never believe any number given to you without double-checking the math.” We all now know that the death rate for the flu is 0.1 percent. See more of the CDC’s numbers on the latest flu season here. For COVID-19, the death rate is somewhere between 0.7 percent in Hong Kong and 4+ percent in China. So, COVID-19 is way worse than the flu, right?

Actually, no, because the math is wrong. The 0.1 percent figure is calculated from the number of estimated cases of flu in the United States. The COVID-19 number is calculated from the number of confirmed tested cases. We all know that testing has been very limited across the board. Even South Korea only tested 280,000 people out of a 60 million population. This makes a huge difference.

It turns out that 33 percent of flu cases are asymptomatic (sound familiar to COVID-19?), and most cases aren’t tested, because most people don’t go to the doctor or the doctor doesn’t test. If you just looked at tested cases, the flu death rate would be around 6–8 percent based upon the best data I can find.

So, if you want to compare the two, the seasonal flu and COVID-19, you have to use the same methodology. It doesn’t mean COVID-19 isn’t bad, but you can’t use the 3.4 percent death rate to model the whole population. If you do that, you are dramatically double-counting.

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