So one of the key metrics for tracking #COVID19 is positivity rate. Today Minnesota reported 745 new cases and 14,791 new tests, for a 5.04% positivity rate, essentially flat.

BUT there’s a problem with this. 1/

2/ That’s 745 new people with #COVID19 versus 14,791 tests completed. But some people take multiple tests! Ideally what we’d want is either PEOPLE with COVID divided by PEOPLE who’ve been tested, or positive TESTS divided by total TESTS.

3/ I discovered this a few weeks ago and have been pressing @mnhealth to share more data so we can calculate an apples-to-apples comparison. I was told they were working on it, and today @mnhealth added “total people tested” to their situation update: https://www.health.state.mn.us/diseases/coronavirus/situation.html#dailyc1

4/ As of today, Minnesota has conducted 1,007,882 total #COVID19 tests. But that represents 820,817 people who’ve been tested. The difference are people getting tested multiple times.

5/ If we divide Minnesota’s 53,692 people who’ve tested positive by its 820,817 people who’ve been tested, we get a *cumulative* positivity rate of 6.5% — higher than the cumulative rate of 5.3% if you divide 53,692 by 1,007,882.

6/ I can’t calculate a correct *daily* positivity rate today because I don’t have a figure for what the total people tested YESTERDAY was. I’ve asked @mnhealth for past data so I can correct this chart. Hoping to get this, but expect it’ll take time.

7/ But I do have data on total people tested from March through June 4, when @mnhealth switched to displaying total tests instead. Add in today’s data point, we can see the relationship between total people tested and total tests over time:

8/ Early on in the outbreak, very few people were getting tested more than once. Today about 20% of tests have gone to people who’ve been tested multiple times. (Some surely more than twice, too.)