It is clear that COVID is spreading in communities in Northern California, and Washington. The time until it is confirmed to be spreading in SoCal is probably a few days. It will always be confirmed *after the fact*, which means it is probably spreading in the SoCal community at the moment, though in the early stages. Outside China cases are increasing exponentially with a doubling time of about 5 days +- which you can read off the graph at several web-sites such as the linked map site (click logarithmic graph on the lower right graph, read off the yellow dots for outside China spread).

I personally view it as inevitable that PUSD will decide to close schools. I don’t know what their timeline will be, but as these are typically committee decisions and there is risk either way (too early vs too late) I expect them to be delayed until the choice becomes obvious. On a doubling every 5 days trajectory, that probably means somewhere in the 10 to 15 to 20 days from now (which would mean somewhere around 800 to 3000 cases in the US). Spring break being Mar 30, I could imagine they’ll try to stay open til the 25th or so, and then not reopen after spring break. Though more pro-active decision making might mean closure in the next 5-10 days or so now that Pasadena has declared state of emergency. All this is more or less my own opinion based on reading the growth charts, and seeing the responses from large organizations canceling conferences and things.

Now, at what point is it actually logical to pull your kids from school? I’m going to do this just for a family with a stay at home parent, because the calculation for lost days of work is much harder and depends on a lot of factors. We can back of the envelope calculate this as follows: Costs of lost days of education is on the order of a couple hundred dollars a day. Let’s say \$20/hr x 6hr/day = \$120/day. If the stay at home parent can provide some of this education, the cost might drop to say \$50/day…

Now, what’s the costs associated with sickness? Let’s just do the calculation of one parent gets seriously ill and dies. For a child in elementary school let’s just put this around say \$10M.

Now, what’s the chance of death if you have definite exposure? It’ll be something like 100% chance of getting sick and 0.5% chance of death (assuming parent doesn’t have underlying conditions and isn’t unusually old)… So the expected cost is \$10M * 0.005 = 50000… So by this logic, you should be willing to avoid that by pulling your kids from school about 1000 days early. Of course, it’s way too late to be 1000 days early, so basically you should pull your kids from school TODAY.

Now, suppose you have a job making \$100k/yr, and you just get cut off from that job. That’s \$385/day (which you don’t take home all of, but whatever). So if you add \$50/day to that for educational loss, you should be willing to pull your kids about 115 days early. It’s also too late for that… So again, pull your kids TODAY.

Any way I back of the envelope this, it’s time to pull your kids from school… I don’t see a big enough flaw in all these calculations that would lead to waiting another 20 days.