How common is it for a Covid test to give a false positive result? A false positive result occurs when a test reads positive, but the person does not have the disease. a) Your Guess: Calculation - Bayes Theorem! Prevalence of the disease matters and the accuracy of the test. Accuracy of a test means that IF a person has Covid, that's the percent chance that person will test positive or IF a person does not have Covid, that's the percent chance that person will test negative. b) Let's look at the numbers of if the Covid Test is 98% accurate and Covid is in 10% of the population. For ease, let's calculate using a population of 5000 people: Disease Present Disease Not Present Totals: Test Positive Test Negative Totals: 10% of population: 500 people 90% of population: 4500 people c) Now if 1% of the population has Covid: Disease Present Disease Not Present Totals: Test Positive Test Negative Totals: d) How common is a false positive in each situation? 10%: 1%: