The_jackalope
The_jackalope's JournalAnother curve fitting exercise
I just graphed the global COVID-19 case data from https://www.worldometers.info/coronavirus/ from Feb 19 to today in Excel.
I fitted two trendlines to the data, second-order and third-order polynomials, both projected out one month. The fit for the second-order trendline is 0.9909, and the projection indicates half a million cases worldwide in a month. The third-order trendline has a fit of 0.9992, and the projection for April 15 is 1 million cases.
My expectation is that the final number will be between the two - closer to the smaller number if social distancing is relatively successful around the world, but closer to the upper number if it is not.
The CFR for resolved cases (recovered+died) is currently around 7%, but has climbed from 6.3% over the last two or three days. The percentage of recovered cases has dropped from 53% to 49% in the same time, meaning that the spread of active cases is accelerating.
No warrantee express or implied, only one per customer, offer void where prohibited, yadda yadda.
A more realistic CFR is in the neighbourhood of 7%, not 1% or even 3.5%
Potential Biases in Estimating Absolute and Relative Case-Fatality Risks during OutbreaksThis section is pertinent to a point I've been trying to get across, with little success so far:
During an ongoing epidemic, at any week w the persons who have died up to time w will not be the only ones to die of the infection among those who became cases by w. The denominator of the CFR (cases) includes persons who have not yet died of the infection, but will do so in the future. Thus the CFR by w will be less than the true CFR. This bias will be particularly severe for infections that are increasing rapidly in incidence and for which the infection–death time interval is long. (my emphasis)
In the current global situation, these criteria are in play. The infections are increasing rapidly, and the infection-death interval is long relative to the rate of infection.
Today (March 12), there are ~128,000 identified infections, of which ~4700 have died and ~68000 have recovered. So 57% of the identified infections have so far resolved in either recovery or death, while 43% (~55300) are still active, without resolution one way or the other. As time goes on, those 55000 active cases will resolve in either recovery or death.
All else being equal, we can expect that about the same proportion of the active cases will die as have died in the first half of the infections that have already resolved. In other words, of the currently infected cohort we have 4700 known deaths, with a similar number yet to come.
If that holds true, there will ultimately be over 9,000 deaths from the 128,000 currently known infections.
The naive calculation of CFR that everyone is using (but still studiously avoiding in favour of the influenza numbers) uses the identified infection number, for a calculation of 4700/12800 = 3.7%. In fact, the probable eventual CFR for today's situation, by the time all currently identified infections have resolved, will be more like 9000/128000 = ~7%.
The fact that there are undetected cases out there does not change this calculation. Those cases are in the same situation as the currently active but unresolved cases. Those cases will develop into symptomatic illnesses at the same rate as those identified but asymptomatic cases today, and will then either recover or die. Along the way they may contribute to the spread through asymptomatic transmission, but the eventual CFR will, again, be unaffected.
If the average trajectory of the individual illnesses remains the same as it is today, the 7% rate will continue to apply. The only way to change the CFR, as far as I can tell, is to change the outcome of individual illnesses on a large scale. Changing the rate of spread will not affect the CFR.
It's important to remember that this calculation is based on a global average of disease trajectories, and when all is said and done, different countries will exhibit different CFRs.
I'm not an epidemiologist, just a guy on the net. That doesn't necessarily mean I'm wrong.
The world is right to be a freaked out. You don't close down Italy or cancel the NBA season over the flu. A 7% CFR is a whole other kettle of carp.
The true death rate at this point is 6.3%
You don't count the active cases. There are 68000 recoveries and 4600 deaths. 4600/72600 = 6.3%
This thing is 30 to 50 times more lethal than the flu.
It's self-quarantine time for everyone.
Profile Information
Member since: Sun Jun 4, 2017, 05:46 PMNumber of posts: 1,660
