The Case Fatality Rate (or Case Fatality Ratio or CFR) is the proportion of people who die from a specified disease among all individuals diagnosed with the disease over a certain period of time.
The Mortality Rate is a measure of the number of deaths (in general, or due to a specific cause) in a particular population, scaled to the size of that population, per unit of time. Mortality rate is typically expressed in units of deaths per 1,000 individuals per year; thus, a mortality rate of 9.5 (out of 1,000) in a population of 1,000 would mean 9.5 deaths per year in that entire population, or 0.95% out of the total.
Thus, for coronavirus, let's assume there are 77,660 confirmed cases of, and 2,663 deaths due to coronavirus in Mainland China. Let's also assume (and sidestep the debate over accuracy) there are 1.3bn people in Mainland China and 200 million under quarantine. With these numbers, depending upon the context, you can get these figures:
Mortality Rate of 2,663 / 1.3bn or 0.0002% or 0.2 people per 100,000 (the context is all of Mainland China).
Mortality Rate of 2,663 / 200MM or 0.0013% or 1.33 people per 100,000 (conxtex is the Rate is conditional upon the people being under quarantine).
CFR of 2,663 / 77660 or 3.4% at this time in Mainland China, without any correction for recovery/"being cured" or timing mismatch (i.e. Not all people in numerator and denominator have been infected or dead for the same amount of time - that would require a cohort analysis).
In fact, the literature on CFRs usually has a qualifier that a CFR is basically "valid" ONLY when the pandemic is through. Thus, these numbers are in flux and can / may / will change from day to day.
The point of my post is to differentiate between the varying rates and ratios and percentages being quoted. Further, while a CFR today isn't comparable directly to a CFR for some other disease that has run its course, I do believe there is benefit in calculating the CFR and making comparisons across countries and time. After all, we keep track of the runs scored during a baseball game even though it ain't over till its over.
I am not a biostatistician nor do I play one on TV. But this knowledge should serve people well during this saga.
Yes, that's why I use completed cases as the denominator in my estimates.
To know the yield of a process I don't need to know how many parts are on the manufacturing floor, I only need to know how many good parts there were and the total number of parts made it out of the shop floor and into final inspection.