Read on Twitter
I honestly don't get the use of "positivity rate" as the most visible statistic in a COVID dashboard. https://protect.purdue.edu/dashboard/ What does this statistic even mean? When you blanket test all members in a population, fine, it means something. 1/4
However, if you are testing only part of the community, it doesn't mean anything unless you're testing people at random. High positivity rate could simply mean you're testing only those showing strong and visible symptoms. 2/4
Low positivity rate could simply mean people are more motivated to get a test because it's recently made more accessible or, say, there's a more visible outbreak in Alaska that's making national news. If the denominator is not randomly sampled, the "rate" is meaningless. 3/4
The only purpose it serves, I suspect, is to control risk perceptions at a low level by making the campus look safer than it is, but this could be self-defeating as people are very sensitive to changes closer to ends of the 0% and 100% spectrum. 4/4
