How the Reverend Bayes is key to coronavirus serology testing

The Reverend Thomas Bayes was an 18th-century Presbyterian minister and mathematician. An important theorem he developed late in his life is now known as Bayes theorem.

Bayesian probability theory specifies how we should update our belief in the likelihood of something given new evidence or data. Bayesian probability is not intuitive and is not well understood by many people, including some doctors.

Consider the case of medical diagnostic testing. We start with a patient who we are concerned might have a particular disease.