Can You Trust a Rapid Test Result? A Look at the Math.

You probably know at this point in the pandemic that if you test positive on a rapid test (and you've used the test correctly–you've got to swab pretty hard!) that the odds are overwhelming that you have COVID and are infectious. You have, no doubt, been warned that a negative result on a rapid test should be taken with a grain of salt, especially if you've been exposed to the virus or you have symptoms. And you might have heard two terms about tests thrown around: sensitivity and specificity, particularly if you've been trying to get a grip on exactly how accurate rapid tests are. As a mathematician, I think knowing a bit more about how sensitivity and specificity are calculated can help you better understand why a positive result should be headed--and a negative test should be read with some caution. The high specificity and rapid BinaxNOW antigen test turnaround time facilitate earlier isolation of infectious persons.