busybee

Rebecca Watson made an excellent video about how the recently-released COVID-19 risk map is not particularly helpful, due to the lack of context provided and the public’s general lack of understanding about how statistics work. It’s well worth watching (and also talks about a few other things, like issues with services like 23andme’s genetic risk factor screening kits). People are apparently using this risk map as a means of justifying going to Thanksgiving gatherings based on “only a 5% infection chance” or the like, which is incredibly short-sighted.

Let’s say that 5% of the population is carrying the disease, and assume that this statistical model is completely accurate. (It almost certainly isn’t, but that’s beside the point.) This means that any time you encounter someone there’s a 5% chance that they’re infected. That seems pretty low, right? For a single encounter, sure. But that doesn’t tell the whole story.

A frequent thing that people want to do in making games or interactive applications is to shuffle a list. One common and intuitive approach that people take is to simply sort the list, but use a random number generator as the comparison operation. (For example, this is what’s recommended in Fuzzball’s MPI documentation, and it is a common answer that comes up on programming forums as well.)

This way is very, very wrong.