Predictive values of diagnostic tests
What is the probability of infection after a positive test result?
In England, people reported over 260 million rapid viral tests for SARS-CoV-2. There have been almost 200 million conducted lab tests.
Diagnostic tests are imperfect. Sometimes, tests give a positive result to someone without an infection. Other times, they suggest a negative answer to an infected person.
How do we calculate the tests’ ‘positive predictive value’ or ‘precision’? That is the probability a…