Charles R. Twardy

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A Covid Puzzle Resolved

In a discussion with @Somensi about excess deaths, I was puzzled by an apparent discrepancy between two sources that have both been reliable, insofar as I can tell:

  • The weekly data on cases, hospitalizations, and covid-attributed deaths.
  • The laggy but solid CDC excess deaths counts/estimates.

Puzzle: December Covid vs Excess Deaths

The basic question from mid-December was how to reconcile this and this:

Graph from showing mid-Dec covid deaths equal or exceeding April deaths. Alternate view, same data.

With this:

CDC excess deaths report showing mid-Dec excess deaths on par with second wave (July) excess deaths, about half the height of April.

(Screenshots are from mid-Dec.)

In short, by early December it was clear that had started diverging wildly from the CDC excess death counts. Two basic theories:

  • covid-tracking was correct - CDC counts would catch up in a month or so.
  • covid-tracking was wrong - this was an attribution blip.

There’s a lot of noise on the thread, but @Somensi, who I don’t know, was also looking at data, and citing a good source. Doomsters like me have been using CDC excess data since April as evidence that the pandemic was real and could not be simple relabeling of flu deaths. Here the same source is cited to say the December spike couldn’t be real.

People on both sides who knew the CDC data understood it had a lag of 4 weeks or so – because it relies on actual death certificates completing all their procedural checks and getting filed. In 2016 it took 10 weeks for 80% of certificates to get filed. CDC now claims it gets to 60% in ~10 days. (There are plenty of people who don’t get the lag – it seems even to have tripped up JHU’s Dr. Briand, at least in her headline claim that there were no excess deaths in 2020.)

Problem: covidtracking is the most thoroughly-vetted weekly data source in the US. They’ve tracked the CDC excess deaths (after lag) the rest of the year. And reliably, their cases –predict–> hospitalizations 4 weeks later –predict–> deaths a few weeks later. The December death spike followed that pattern. Plausibly, CDC was just lagging.

Problem: CDC 4 weeks back should be pretty good, and it looked nothing like April. As my correspondent said, CDC data “would have to be lagging by an unprecedented amount.”


It’s obvious once you see it.

That death spike (swoop?) at the end is super fast. If you hover over the attributed deaths chart from covid-tracking, you find that the Nov. 14 cases are exactly in line with their July numbers, about half their April numbers. And in line with the mid-Nov. CDC numbers. The steep rise is mostly in the last 4 weeks.

Choosing Nov.14 as the comparison shows attributed deaths on par with the CDC excess deaths. Resolved.


As of Dec. 23, we can look at how the CDC data has changed. Data should be pretty complete through Nov. 21. We see that Nov. 14 is now about 1,000 higher than before (and than the July peak), and Nov. 21 about 2,000 higher than that.

CDC excess deaths on Dec. 23, highlighting Nov. 21 data from four weeks ago.

Not a swoop yet, but basically on par with the covidtracking chart week-for-week. Here that is again from today, highlighting Nov. 21. (The bold line is the 7-day moving average, a far better comparison than the daily total.)

Covidtracking deaths chart highlighting Nov. 21.


We should definitely expect the CDC excess deaths count for December to reach April levels.