COVID-19: Down the Rabbit Hole of Death Rate Calculations - Part 2

Note: Written June 24th.

I think firstly we need to get our fatality calculation described and agreed upon. For simplicity sake, let's use the CDC, since it is the CDC's IFR of 0.26% that started this blog post.

The CDC has an educational lesson called:

Principles of Epidemiology in Public Health Practice, Third Edition An Introduction to Applied Epidemiology and Biostatistics

Lesson 3: Measure of Risk, Section 3: Mortality Frequency Measures is where we will start. Let's go down to close to the bottom and look at the Case-Fatality Rate:

Let's next look at the example they give:

If we can agree on this calculation - from the CDC - then the Case Fatality Rate CFR is the number of deaths divided by the number of cases. I will get into the lag time from death to cases but for now, this is a crude way of calculating what the CFR is.

A few days ago I went to get data from the WorldoMeters site. Using that data, number of deaths and number of cases on June 20th, this is how the CFR calculates:

That CFR calculated, using the CDC definition and methodology, is quite a bit higher than 0.26%. So what gives?

What does a "case" and "death" mean as it relates to COVID-19? The Worldometers site defines a "case" as follows:

We will get back to that second to the last sentence in a bit. Right now let's make sure we can agree on what a "case" and "death" is when calculating the Case Fatality Rate (CFR) for COVID-19. Here is what the change they refer to for the CDC:

What that means is that we are getting closer to a true number when the reported cases and deaths also include not just confirmed cases based on testing only, but ones where a reasonable certainty of it being COVID-19 is present. 

This means that my calculation identified previously include both. So why is the CDC's IFR almost 10 fold lower than the CFR I calculate.

Deeper we go into that rabbit hole...

On to Part 3.