Our state health director says that when you test more, you get more cases, accounting for the increasing numbers of COVID-19 diagnoses over the past few weeks. However, it is not just the absolute number of cases, it is the percentage of positives among those tested that is going up. One learns in statistics class that the proportion of positives in a valid sample is not a function of sample size, but a function of population incidence. More testing does not produce a higher proportion of positives - if the incidence remains the same the ratio of positives to negatives in the sample remains the same even at 100% population testing. Absolutely, mathematically, the incidence of COVID-19 in Arizona is increasing, not due to testing but due to spreading of the virus, as mitigation practices are loosened in the name of economics. We still have no treatment and no cure. The fatality rate remains between 5 and 10% of those infected. How many deaths will be economic?
David Vernon, PhD in Life Sciences and an MS in statistics
Disclaimer: As submitted to the Arizona Daily Star.
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