More specifically, testing ten to twenty percent of the students weekly will mean that cases are likely to be missed. How likely? Well, here’s the probability that, for a given number of infected students in a classroom of twenty total students, every positive case will be missed given a certain percentage of tested students (10%, 20%, 50%):

Here’s the same for a class of thirty students:

Not only is this the chance you’ll miss every student, but this also assumes that the tests do not yield false negatives (i.e., miss infected students), so this is a best case scenario.

This is why I argued in this post that D.C.’s testing regime is better than no testing, but not by that much.

If the Mayor and the Council are going to crow about the budget surplus, maybe spend some of it on more testing? Just a thought.