Use the drop-down menu to look at the progression of an area's case positivity rate, which is the percentage of people tested for coronavirus, who have received positive results. NBC5 Investigates is using the Illinois Department of Health's numbers, and the IDPH formula, for computing these rates. However, the state uses a slightly different rate -- the "positive test rate" -- which is the percentage of tests that are positive for coronavirus, out of all tests conducted. This counts repeated tests on the same person, and is nearly always lower than the "case positivity rate" listed here.