Whenever you do a math calculation, it’s a good idea to do a sanity check. The goal is to do a quick test to determine whether the answer could possibly be true. Not that it is true, but that it could be true. Or, to put it another way, to verify that it isn’t obviously false.
For example, if you were doing a rough estimate of the circumference of the earth and came up with 2500 miles, a sanity check says “wait a minute, that’s less than the distance from here to New York, so it can’t be the right answer.”
Needless to say, an absence of sanity checks happens pretty frequently in Covid discussions. I recall three weeks ago (which is basically forever when it comes to this crisis), someone latched onto an analysis of antibody testing done in Santa Clara county that indicated that far more people may have been infected by coronavirus than previously thought. This person did some ‘back of the envelope’ math and came up with a death rate of 0.00014, which is remarkably low. Great news!
But, they didn’t take the next step, which is to do a sanity check. Here are a couple they could have done: a) as of April 17 (the date the study was released), the USA stood at 37,000 deaths. To have a death rate of 0.00014 means that 80% of the country had already been infected (37,000 / .00014 is 80% of 330 million). Doesn’t seem likely. b) Take that death rate, and multiply it by 330 million (the population of the US). The result is around 46,000. That means that if everybody in the country got infected, there would a maximum of 46,000 deaths. At the time we were at 37,000 and climbing at about 2000 a day, so even back then that number seemed ludicrous. And of course, by now we’ve blown way past that number.
Who knows if this guy made a math error, or a logic error, or what? If he had just done a sanity check, we wouldn’t have to guess why, because he never would have posted it in the first place.
