First, let me say. Stay safe, wash your hands and avoid sick people. But I wanted to do some digging on the math, “the denominator problem” as Dr. Fauci stated.
Lots of news organizations want to push the panic button. “ten times worse than the flu” and they jump all over it. But the same denominator problem still exists. I know that we can only deal with the numbers that we have and that news organizations are quick to latch on to anything spectacular to drive audience. So lets look at what we have.
We have a Flu metric that is based on annual projections of the entire us population with years of immunity and antibodies (those would be on our insides). We can therefore project that in a given year 10% of population will come down with the flu, a half a million will visit a hospital and 30,000 or more will die. Nasty; and that gives us the .1-.2% mortality rate.
With this new virus we were originally looking at a 6.8% mortality rate in China…WOAH. But this number was not of the whole population or a projection of 10% of a million people. This was of the original group in China the presented symptoms and were hospitalized. Since this first population, there is now LOTS of news coverage, better hygiene, more tracking and we are now catching the symptoms earlier. The rates in China have now dropped t(reported by China) to .7% in other cities. That new population is still based on those people presenting to healthcare workers or those with symptoms; not a whole population. But that shift from originally very sick to those presenting after the news coverage started is a important change in the selection bias of the population.
So how do we compare these numbers if we do not have the knowledge to estimate COVID-19? We do have flu numbers, years of them. We have the rates of flu for those that present to medical professionals and those hospitalized. Those numbers would seem to better represent an apples to apples comparison to the pattern being observed above.
For the 2018 flu season, there were an estimated 35 million cases. Of those, 490K were hospitalized, accounting for 34,157 deaths. That is a 6.9% mortality rate for those that were hospitalized due to symptoms. Right in line with the initial population of Hubei province. Like Cornavirus, the flu tends to be far worse in the more seasoned population. Within that group the mortality rate after hospitalization is 9.1%.
So lets’ take a step back and move on from the initial outbreak and look at more expansive testing. If we expand the flu numbers to include those that visited a medical professional with flu-like symptoms we expand our universe (for 2018) to 1.7 million people in the US. Same death toll accounts for 2.0% mortality rate. We seem to be trending lower than that as of today.
Though we are between .7% and 1.4% mortality for COVID-19, we still have a denominator problem. We have not yet conducted population-wide studies. Some recent numbers begin to shed some light. 80% presenting with mild symptoms. It looks to me like the initial population of acute symptomatic people was following the universal 80/20 rule. 80/20 = 20% and 20% of 6.8% is 1.4% … right in line with the flu.
What I am looking forward to learning (numbers not people, well wishes on all the people) is two things; the full population test of the Grand Princess and a full antibody screening of populations for exposure. Those will inform us about non-symptomic carriers and the overall contagiousness of the virus.
These new numbers will help us a lot in finding the correct denominator(s). Until then, let’s try to use some prudence and work to compare like populations. We may look back at COVID-19 as just another nasty flu. Better safe then sorry. A pound of prevention. I get it. But we are wreaking havoc over the world’s economies, hurting business, hourly workers and creating a general panic. I get that it is new and unknown, but the news should be helping us make sense of the numbers. Instead they breed the panic, show the empty shelves, and ignore the progress. Yes, we need to remind ourselves, to wash your hands and avoid sick people… with the Flu; that thing is nasty and kills people.
UPDATE 3/20: Does not look like those in charge are going to test everyone on the Grand Princess. We will not be able get the full population numbers that would truly inform the denominators. Mobile testing units and New Rochelle, New York may help inform the metrics.
UPDATE 3/26:
Seems others beginning to say the same; using math versus panic.
In the coronavirus pandemic, we’re making decisions without reliable data [STAT]
FSI – Is the Coronavirus as Deadly as They Say? [Stanford references WSJ]
Is the Coronavirus as Deadly as They Say? – [WSJ]
What do we know about the risk of dying from COVID-19? – [Our World in Data]
UPDATE 3/30:
The mystery of the true coronavirus death rate [Financial Times]
“Arguably the biggest unknown about Covid-19 is the true number of people worldwide who have contracted the virus. Without that information no accurate death rate can be calculated.”
Coronavirus death rate: What are the chances of dying? [BBC News]
“On 17 March, the chief scientific adviser for the UK, Sir Patrick Vallance, estimated there were about 55,000 cases in the UK, when the confirmed case count was just under 2,000. Dividing deaths by 2,000 will give you a much higher death rate than dividing by 55,000.”
Edited for Bias 
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