Covid-19: Apples and Oranges

We’ve all heard the numbers reported about Covid-19 deaths in the US. We’re also familiar with the annual mortality statistics for the flu. Indeed, it’s common to hear the two sets of numbers compared to each other in order to put the Covid-19 pandemic in perspective.

Only…it appears we’ve been comparing apples and oranges.

The reported Covid-19 deaths are ones in which it played a significant role in death, as determined by actual observation and testing. Intuitively, that’s what most of us would expect a “deaths due to disease ‘X'” number to mean.

But the reported flu mortality numbers are different. Not because anyone is trying to mislead people. They’re different because experts (a) know a lot about how the flu kills or contributes to death and (b) also know that no reporting system will accurately capture the actual number of cases where flu was a contributing factor in death. All that’s reported are the ones where it’s directly observed that flu played a key role.

So the experts do the natural thing and extrapolate from those directly observed numbers to a here’s-what-the-number-would-be-if-we-caught-everything estimate. That’s what gets reported as the “annual deaths due to the flu”. The difference is enormous: the reported annual death attributable to flu number is about five times higher than the directly observed number.

For Covid-19 it’s too early to do the same kind of extrapolation1. Instead, the reported data is essentially just the directly observed deaths.

Here’s directly-observed flu deaths compare to directly-observed Covid-19 deaths so far:

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The orange bar are the Covid-19 deaths reported on the Center for Disease Control website. The red bar is the number being reported by most media outlets as the current Covid-19 deaths. I’ve included both because there’s a reporting lag in getting the data through the CDC system that I can’t adjust for.

Whether the orange bar or the red bar is the “right” number is less important than this: both are much higher than the directly-observable flu deaths.

I learned about this measurement discrepancy from an article in the Washington Post2, not a medical or scientific journal. So it’s possible it’s in error.

But my gut tells me otherwise. Extrapolating flu deaths makes sense because we know a lot about the flu. Not being able to extrapolate Covid-19 deaths the same way also makes sense. It’s too soon.

So take this information with a grain of salt.

But…assuming it’s correct I think it goes a long way to explaining why the experts — who more than likely understand the difference between the “apple number” and the “orange number” — were so concerned about the Covid-19 death rate, and pushed for significant public health constraints.

  1. Although as we learn more about the disease attempts are being made to do those calculations 

  2. which quoted a number of experts and had links to their data sources 

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