US Fatality Rate - A Closer Look
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From link provided below:
"The case fatality rate (CFR) represents the proportion of cases who eventually die from a disease.
Once an epidemic has ended, it is calculated with the formula: deaths / cases.
But while an epidemic is still ongoing, as it is the case with the current novel coronavirus outbreak, this formula is, at the very least, "naïve" and can be "misleading if, at the time of analysis, the outcome is unknown for a non negligible proportion of patients.
In other words, current deaths belong to a total case figure of the past, not to the current case figure in which the outcome (recovery or death) of a proportion (the most recent cases) hasn't yet been determined.
The correct formula, therefore, would appear to be:
CFR = deaths at day.x / cases at day.x-{T}
(where T = average time period from case confirmation to death)
This would constitute a fair attempt to use values for cases and deaths belonging to the same group of patients.
One issue can be that of determining whether there is enough data to estimate T with any precision, but it is certainly not T = 0 (what is implicitly used when applying the formula current deaths / current cases to determine CFR during an ongoing outbreak)."
They go on to use "a conservative estimate of T = 7 days as the average period from case confirmation to death."
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Now note the current fatality rate for the US, shown below for cumulative cases/deaths on the dates shown:
Mar 7: 4.5%
Mar 8: 3.8%
Mar 9: 3.5%
Mar 10: 3.1%
Mar 11: 3.0%
Mar 12: 2.5%
Mar 13: 2.2%
Mar 14: 2.0%
Mar 15: 1.8%
Mar 16: 1.8%
Mar 17: 1.7%
Mar 18: 1.6%
Mar 19: 1.5%
Mar 20: 1.3%
Mar 21: 1.3%
Mar 22: 1.3%
Note that the fatality rate shown is a) dropping due to the acceleration of the testing regime and b) is lower than the actual fatality rate comparing a stable cohort of cases with their eventual outcomes (due to lag in deaths vs cases as explained above).
Here I provide an adjusted fatality rate based on the methodology discussed above. I use a more conservative value of T = 5. That is, adjusted fatality rate = (cumulative deaths to date/cumulative cases 5 days ago). With that the numbers look like this:
Adjusted US Fatality Rate (T=5)
Mar 13: 6.9%
Mar 14: 6.3%
Mar 15: 5.8%
Mar 16: 6.1%
Mar 17: 6.0%
Mar 18: 6.7%
Mar 19: 7.2%
Mar 20: 6.8%
Mar 21: 6.5%
Mar 22: 6.5%
Note that with this adjustment the fatality rate is relatively stable around 6 - 7 %. This is likely to be a truer representation of the percentage of diagnosed cases which will ultimately prove to be fatal. Of course, as with all such fatality rates, it refers to the percentage of those diagnosed with COVID-19 rather than the percentage of all individuals who have actually contracted COVID-19.
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https://www.worldometers.info/coronavirus/coronavirus-death-rate/#days