I honestly don& #39;t get the use of "positivity rate" as the most visible statistic in a COVID dashboard. https://protect.purdue.edu/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& #39;t mean anything unless you& #39;re testing people at random. High positivity rate could simply mean you& #39;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& #39;s recently made more accessible or, say, there& #39;s a more visible outbreak in Alaska that& #39;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