Since the beginning of the pandemic, ‘test, test, test’ has been the key message from epidemiologists, infectious disease specialists and healthcare professionals alike. But how does a country know if it’s doing sufficient testing? Or that it’s catching enough of the asymptomatic cases? Nicola Davis speaks to Prof Rowland Kao about the positivity rate, a value that can help to answer some of these difficult questions. Help support our independent journalism at <a href="https://www.theguardian.com/sciencepod">theguardian.com/sciencepod</a>
