Critiquing the Frequency and Prevalence of COVID19 Cases: Leading with Randomization

Please keep in mind, the reports on COVID19 that we are getting are based on the frequency of confirmed cases. At best we know how frequently these tests have been administered and how frequently they returned positive or negative results. We also know, of those testing positive, the frequencies of resolved cases and death. Notwithstanding our reliance on testing, the authorities can tell us little or nothing about the prevalence of COVID19. For instance, in the U.S. population of about 328 million, exactly how widespread is COVID19 infection?

In San Diego County, for example, as of May 18, 2020, there have been 108,426 tests with 5,946 returned positive and 211 deaths. This is about a 5.48% testing confirmation rate. The population of San Diego County is 3.3 million. Theoretically, if the entire population undergoes testing, at a positive test rate of 5.48%, the result would be 180,970 active COVID19 cases. At a death rate of 3.55%, this would mean3,848 deaths among the pool of confirmed cases.

However, these brief calculations neither take into account the number of false negative tests, including the number of people who have COVID19 but show no symptoms; the number of false positive tests; nor the number who had COVID19 but died from associated complications, such as heart, liver, or kidney failure. A prevalence study would need to include such factors.

It is critical for those who want to know to grasp the difference between frequency and prevalence; doing so will make us more aware, so we can better fulfill our duties to serve and protect ourselves, our families, and our communities. Here is a helpful heuristic: Frequency is how many times you deposit money in your savings account; whereas, prevalence is how much money you have in your savings account. Applying this heuristic, we learn that frequency describes the number of times COVID19 infection occurs over the number tested; whereas; prevalence describes the number of times COVID19 infection occurs over the number of times an infection could possibly occur.

How ought we go about determining prevalence, considering the factors that we must consider? One way is to test everyone in the population in which we are interested. A more efficient way is by testing a representative sample from among the population of interest, and the most cost-effective way to secure a representative sample is via randomization. Randomization is the most powerful way to control population differences, including the number of asymptomatic-types and those who had the disease and recovered.

Reflection on the difference between frequency and prevalence can lead to better understanding and thus greater capacity to critique COVID19 reports, become self-aware, and protect and serve according to reality, not political rhetoric. Critical thinking requires both knowledge and courage!