Arizona Positive Test Percentage Downtrend Mystery Solved
As noted in yesterday's weekly numbers update , I have been puzzled about why the positive test percentage in Arizona has been consistently trending down when new cases have been consistently trending up. After all, it takes a test to identify a case, so it seems like the positive test percentage should go up as the new case rate goes up. The ASU Biodesign Dashboard has data on raw numbers of positive a negative tests. So I downloaded that data and had a look. One thing to note is that the number of tests has gone way up over the last month. On August 6 the seven-day total was about 66K tests. By August 28 the seven-day total was about 97K tests—almost a 50% increase. Of course, more testing don't explain the mystery downtrend by itself. But things become clearer when we look at the trends in positive vs. negative tests (dotted lines are trendlines): As we can see, both positive and negative tests are trending upward, but negative tests are t...