Wei_Dai's Comments

April Coronavirus Open Thread

I was suspicious of the IHME model several days ago when I first saw it, but couldn't find a detailed description of their methodology. (It's really well hidden, and doesn't even appear in their FAQ section.) Finally found it yesterday, noticed the "similar to Wuhan" assumption, then saw the page criticizing it linked in the comments section for the paper.

April Coronavirus Open Thread

The IHME Covid19 Model is Dangerously Flawed:

Flaw #1: The model assumes the measures most states are taking now will be as effective as the lockdown in Wuhan

The model assumes, without evidence or justification, that if we take 3 of the following 4 measures (school closings, closing non-essential services, shelter-in-place order, major travel restrictions) it will “be enough to follow a trajectory similar to Wuhan”. Many newspaper articles have covered the extreme measures enacted in Wuhan, but I will summarize them here:


Flaw 3: The model chooses not to incorporate an increased mortality rate for Covid19 patients unable to receive medical care due to overwhelm of the health care system.

Peter's COVID Consolidated Brief for 2 April

According to my calculations from https://covidtracking.com/data/us-daily, the number of tests per day in the US has stayed flat since a week ago (97,806 on Mar 26, 100,989 on Apr 1), while the positive rate has gone from 17% to 26%. If more tests were being done to keep pace with actual infections, the curve for the US wouldn't be bending so much.

Something similar may or may not be happening elsewhere, but we can't really trust "projecting the curve forward" without looking into more details.

What is the safe in-person distance for COVID-19?

Another reference (being reported in the news): Turbulent Gas Clouds and Respiratory Pathogen Emissions - Potential Implications for Reducing Transmission of COVID-19

Given various combinations of an individual patient’s physiology and environmental conditions, such as humidity and temperature, the gas cloud and its payload of pathogen-bearing droplets of all sizes can travel 23 to 27 feet (7-8 m). [...] Eventually the cloud and its droplet payload lose momentum and coherence, and the remaining droplets within the cloud evaporate, producing residues or droplet nuclei that may stay suspended in the air for hours, following airflow patterns imposed by ventilation or climate-control systems.

So indoors basically no distance is safe, outdoors maybe 10 meters is safe if people aren't up/down wind of each other.

Open & Welcome Thread - February 2020

I did sell some of the puts, but not enough of them and not near enough to the bottom to not leave regrets. I definitely underestimated how fast and strong the monetary and fiscal responses were, and paid too much attention to epidemiological discussions relative to developments on those policy fronts. (The general lesson here seems to be that governments can learn to react fast on something they have direct experience with, e.g., Asian countries with SARS, the US with the 2008 financial crisis.) I sold 1/3 of remaining puts this morning at a big loss (relative to paper profits at the market bottom) and am holding the rest since it seems like the market has priced in the policy response but is being too optimistic about the epidemiology. The main reason I sold this morning is that the Fed might just "print" as much money as needed to keep the market at its current level, no matter how bad the real economy gets.

What is the safe in-person distance for COVID-19?

I was thinking of thresholds that were more like “at least 12 feet apart, maybe 20 feet”, with nobody touching any objects.

My point is that since 45 out of 60 people were infected and they were spaced out, the farthest person infected in that group must have been quite far from the source of the infection, and keeping a even longer distance to be safe is probably impractical for most indoor spaces.


(Also, I’m assuming this is all outdoors)

Didn't notice this part earlier. I would be much less worried outdoors where virus particles are more likely to disperse instead of hang around, but don't have any quantitative answers to offer.

What is the safe in-person distance for COVID-19?

From "A choir group had 60 people show up for practice. Now 45 are sick.":

Ruth Backlund, a co-president at the Skagit Valley Chorale, said the group was monitoring public health guidelines at the time of the practice and had asked people to stay home if they showed even minor signs of illness. The group gathered in rows facing a piano and a choir director. They were all in individual chairs and had space to keep separated. Ms. Backlund had made sure there were extra soap dispensers in the bathrooms for people to wash their hands.

“Nobody was sick. Nobody touched anybody. Nobody shook hands. Nobody hugged everybody like you might do in a group. There was none of that,” Ms. Backlund said.

Given that they were spaced out and 1 asymptomatic person probably infected all 45 out of 60 in what must be a reasonably large room, it seems just impractical to keep sufficient distance to be safe indoors.

March Coronavirus Open Thread

Does anyone have thoughts on the recent Oxford study that claims that only a very small minority of infections lead to hospitalization or death, and that >50% of the UK population is already infected?


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