The UK's randomised coronavirus trials are a global success story | David Spiegelhalter and Anthony Masters

For more than a year the Recovery programme has used the NHS to test many Covid treatments, saving lives worldwide

As it is a novel disease, inevitably there have been numerous suggestions for treatments for Covid-19, ranging from herbal tonics to the anti-malarial hydroxychloroquine, as advocated by the former US president. The question is: what treatments work best?

It is not enough just to compare what happened to people who did or did not have the treatment, which may, for example, have been given to healthier patients. The only reliable method is to allocate volunteers at random to either receive the novel treatment or a control, and, if possible, neither they nor the medical team know which. Randomised trials reduce statistical biases and, if they are large enough, researchers can robustly say whether the intervention helps.