The Health Minister Matt Hancock promised the UK would carry out 100,000 coronavirus tests a day by the end of April. The question of just how dangerous the new coronavirus really is, is absolutely crucial. If it's high, there could be dreadful consequences if the lockdowns are relaxed. So why is the fatality rate so difficult to calculate - and is it true that being obese makes Covid-19 10 times more dangerous? Tim Harford investigates the figures as he ascertains whether Hancock's target was met
