In Which Math is Still Hard

 Posted on October 18, 2014 in Uncategorized

I've written here several times, under the category "math is hard," about Americans' innumeracy with regard to risk and danger. I have a theory:

  1. Americans overestimate the danger (risk times harm) of things that they are willing to do something about (terrorism!), and underestimate the danger of things that they are not willing to do something about (obesity!).

  2. The government, meanwhile, has an interest in overstating the danger of things that it is profitable for corporations to do something about (terrorism!) and understating the danger of things that it is unprofitable for corporations to do something about (obesity!).

There are 8,000+-about 2^13-Ebola Zaire cases; that number is doubling monthly. There are 2^33 people on earth, give or take. That's 33 months from one case to everybody being infected, at the current rate. We've used up thirteen of those months; we have twenty months left. Of course the current rate of infection can't be sustained-the virus might not spread as fast in more affluent countries with their indoor plumbing and their medical care, ((Or it might:

  1. 9/24: Duncan symptomatic.

  2. 9/25: Duncan goes to hospital. Is sent home.

  3. 9/28: Duncan returns to hospital via ambulance.

  4. 9/30: Officials confirm that Duncan tested positive for Ebola.

  5. 10/8: Duncan dies.

  6. 10/11: Pham tests positive for Ebola.

  7. 10/15: Vinson tests positive for Ebola.

So the first known Ebola case was known in Dallas on September 28th. Seventeen days later, there were three known cases. That's equivalent to doubling every ten or eleven days-in a state-of-the-art hospital in a modern city among people who knew that Duncan had Ebola, and how to avoid catching it. We should know in the next week-t+25-whether Duncan infected other people before being admitted to the hospital; we should know in three weeks whether Pham or Vinson infected anyone before testing positive.)) and at some point the population becomes sparse enough that the survivors aren't hanging out with each other much anymore.

It can spread like the common cold flu, it doubles every month, and it kills 70% of the people it infects. ((It's not very good at its job, which is to replicate. But it is good at killing its hosts.)) How do you stop this world-changing bug?

If you don't already have an off-the-shelf solution (and we don't-see fn1), it seems obvious that you buy some time by slowing it down. You quarantine everyone who wants to enter the U.S. after having been in the most-infected countries in the last thirty days. ((This is different than the cargo-cult solution of barring flights from the most-infected countries. Airplanes don't carry viruses, people carry viruses.))

But there's not much money for the corporations in a quarantine, so the government plays down the danger posed by Ebola. And the Americans who are willing to do something about it (quarantine!) overestimate the danger while the Americans who aren't willing to do it (it wouldn't work!) underestimate it.

The raw numbers-doubling every 20-30 days; 70% mortality-seem pretty compelling to me. Do I overestimate the danger? It's possible, but if Ebola cases double in eleven days in a hospital in Dallas, I think it's reasonable to be extremely concerned about what's going to happen when it hits the Harris County Jail, and to look to the government to at least try to delay that catastrophe.

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