Am I missing something here? This estimate seems off by several orders of magnitude!

A reporter writes:

I’m writing about a new preprint by doctors at Stanford University and UCLA on relative COVID-19 risk, in which they assert the risk is much less than most people might think. One author in an interview compared it to the risk of food poisoning. It’s a preprint so it’s obviously not fully baked yet, but it’s out there. Copying a link below, it’s not very long. Just wanted to ask your thoughts on the soundness of the science and their conclusions.

From the abstract of the linked article:

Among the 100 most populous US Counties, for the week ending May 30, 2020, the median probability of COVID-19 infection transmission is 1 infection per 3836 unprotected community-level contacts. For a 50 to 64 year old individual, the estimated median probability of hospitalization is 1 hospitalization per 852,000 community level person-contacts and the median probability of a fatality is 1 fatality per 19.1 million community-level person-contacts.

I did a quick look-up of the U.S. numbers and got these numbers for ages 55-64: 11439 deaths out of 42 million people. That’s a death rate of 1 in 4000.

If it’s 1 in 4000 people, and the fatality rate is 1 per 20 million person-contacts, that would mean that each person has roughly 5000 person-contacts. 5000 seems like a lot to me! I guess you can get to 5000 by saying that the epidemic has been happening for about 100 days, with 50 contacts a day. That still doesn’t seem quite right. For one thing, even if you do have 50 contacts a day for 100 days, a lot of these will be the same people over and over, and most of them are not exposed. The numbers just don’t seem to add up.

Indeed, the numbers here seem soooo wrong that I feel like I must be missing something here.

Could someone explain? If I’m completely wrong here, this would be a good teaching moment!

One of the hardest things about statistics is that you can never be completely sure of yourself. The hivemind is a big help.

P.S. Michael Jetsupphasuk sends along this picture of a friendly cat in Turkey, which he says is maybe the best place to be an outdoor cat.