The number that I use to track the virus crisis is the Three Day Death Reproduction Rate. It sounds ghoulish, and it is. It also is a lagging indicator. I wish I had some other indicator. But I do not trust case numbers, because testing criteria are undergoing constant revision.
The 3DDRR is calculated using the data from this site, which is updated every day late in the afternoon, eastern time. It gives the total number of deaths as of each date. The 3DDRR for, say, March 29, is the total number of deaths on March 29 (2428) divided by the number on March 26 (1163), which gives 2.09.
We can say that if the 3DDRR stays close to 2, then that is awful. If it stays over 1.1, then that is still pretty bad. If it is just barely over 1, say 1.002, then that is better. Getting below 1 would require resurrections.
So for all the dates from March 20 through today, we have
| Date | 3DDRR |
|---|---|
| 3-20 | 2.43 |
| 3-21 | 2.43 |
| 3-22 | 2.49 |
| 3-23 | 2.15 |
| 3-24 | 2.48 |
| 3-25 | 2.26 |
| 3-26 | 2.47 |
| 3-27 | 2.27 |
| 3-28 | 2.18 |
| 3-29 | 2.09 |
| 3-30 | 1.92 |
| 3-31 | 1.91 |
| 4-1 | 1.94 |
| 4-2 | 1.97 |
| 4-3 | 1.86 |
| 4-4 | 1.77 |
The trend is in the right direction, but the 3DDRR is still disturbingly high. It would be nice to see, say, 1.5 by April 7, 1.3 by April 10, 1.1 by April 13, and 1.002 from April 16 on. That would raise April 4ths total deaths of 8314 to 17,834 (exactly, right?) on April 13, with slow increases beyond that.
That is a numerical scenario, but it is hard to know what has to happen in the real world to achieve that. Presumably it would require a continued reduction in the spread rate of the disease, along with improvements in triage and treatment.
The problem is that even in such an optimistic scenario, we won’t know how much of the lockdown policy was needed to achieve it. I keep saying that we need experiments in order to better understand the spreading process, but no one listens.
I don’t think it’s literally true that no one’s performing experiments or random testing; see the section “We’re learning what we need to know to respond intelligently” at this post from 80,000 Hours:
Good news about COVID-19 – 80,000 Hours
Who would you want to listen to you and how are you measuring whether anyone is listening?
Your measure has some clear advantages, and seeing a decline is certainly encouraging. One characteristic of the measure to keep in mind, though, is that it comes with a significant lag. If incubation following infection can last 2-14 days, how long is it from exposure to a death that shows up in 3DDRR? Two weeks? Three? A month? If we try something that reduces exposure, that is a disappointingly long time to wait for results.
Speaking as someone who’s spent the last month forecasting this, I’ll offer a couple of points.
Death numbers really are lagged from 20-24 days. So the best case numbers you’ll see on April 16 were locked in by the policies and behaviors around March 25 (give or take). That was of course forever ago. This NYTimes piece (https://www.nytimes.com/interactive/2020/us/coronavirus-stay-at-home-order.html) gives a picture of what states were sheltering in place by then; you shouldn’t find this encouraging.
You might compare your hoped-for 3DDRR’s to those projected by the IHME at https://covid19.healthdata.org/. This is the model the federal government is using. It’s not perfect, many epidemiologists seem to think it’s overly rosy, the authors themselves acknowledge that the uncertainty intervals are uncertainty “on top of a best case scenario” (more or less). Their 3DDRR’s are all much bigger than the ones you’d hope for, with 3DDRR’s above 1.002 stretching into June.
ps. I’ve been a fan of your writing for years. Thank you for so many wonderful thoughts.
If there is a 3-week delay between policy and 3DDRR improvement and there was some improvement starting near the end of March, then doesn’t that mean that the mild measures in place near beginning of March had at least some effect (though not enough)? Furthermore, if by Apr 13, the 3DDRR has declined to 1.003, then would that imply that the policies in place around Mar 25 were sufficient and the ones put in place subsequently were unnecessary?