>case fatality rate: the number of deaths due to a specific disease as compared to the total number of cases of the disease. [0]

You can't take a case into account until you know its outcome. What am I missing?

0. https://medical-dictionary.thefreedictionary.com/lethality+r...

Take a hypothetical disease A that started spreading on Jan 1st. It takes a patient 1 month to recover from A, while it only takes 7 days for A to kill. We perform a calculation on Feb 9th to determine A's case fatality rate.

The correct way to calculate A's case fatality rate would be to select a cohort, Group B, for example: everyone infected in the first week. And calculate:

(deaths in Group B by Feb 9th) / (deaths in Group B by Feb 9th + recovered in Group B by Feb 9th)

An incorrect way to calculate A's case fatality rate would be:

(deaths by Feb 9th) / (deaths by Feb 9th + recovered by Feb 9th)

This is incorrect because "deaths by Feb 9th" includes all deaths from people infected between Jan 1st and Feb 2nd, while "recovered by Feb 9th" only counts the recovered patients who were infected between Jan 1st and Jan 9th. The above equation basically expands to:

(deaths in Group C by Feb 9th) / (deaths in Group C by Feb 9th + recovered in Group D by Feb 9th)

Where:

Group C: infected between Jan 1st and Feb 2nd

Group D: infected between Jan 1st and Jan 9th

Since disease A is spreading exponentially, it's clear that Group C is a few orders of magnitude larger than Group D.

Official mortality rate is 2.1%. Deaths per confirmed infections. And yes, the WHO isn't that stupid to count cases that aren't decided yet. And yes, they are smart enough to take the appr. three weeks it usually takes until death into account.

No idea where you got that 30% from. Even in Wuhan, with its medical infrastructure close to the breaking point, we are talking about 4.9%.

>where you got that 30% from

According to https://coronavirus.app/ we have 34955 infected, 726 dead, 2287 recovered as of now. Total resolved cases are dead + recovered, which is 3013. Fatality rate is 726 / 3013 = 24.1%. At the time of my original post it was 30%.

Just checked the last Situation Report from Feb. 7th from the WHO:

31,211 confirmed cases and 637 deaths in China. Makes a rate of roughly 2.04%. And I trust the WHO to get the calculation behind that right.

That's exactly what I don't understand. Logically, wouldn't deaths typically lag diagnosis by some amount? If so, we would expect the death rate to be higher than current deaths/cases because we need to use the confirmed cases from some number of days ago. That number of days being the average time between someone being diagnosed and dying.

Another stat is that there are roughly 700 deaths and 2400 recoveries, which would indicate a mortality rate of 23%. Of course, this suffers from the same delay issue as the 2% calculation (T_death < T_recovery). But the possible range is 2% < M_rate < 23%

https://www.worldometers.info/coronavirus/#repro

Your intuition is right but it's complicated.

This paper gives a discussion of different biases:

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4504518/

There's a standard paper on this topic the authors I forget atm but all estimates will be biased. The best estimates are sort of unintuitive and account for estimated time-to-death and the time since diagnosis.