Every death is a tragedy for grief-stricken families, but every set of statistics is an opportunity to understand the virus and the disease Covid-19 a bit more. In fact gathering these data, quickly and accurately, is a priority at the moment, up there with developing a vaccine and rolling out widespread testing. Gareth Mitchell discusses, with, David Spiegelhalter, who is the Winton Professor of the Public Understanding of Risk in the Statistical Laboratory at the University of Cambridge, why it’s so hard to measure coronavirus fatalities. The Covid-19 pandemic is unprecedented in modern times. There will no doubt be years of debating over who managed the outbreak the best, which tools and actions were implemented at the right time and in the right way. One small, but important part of dealing with the viral outbreak is contact tracing – discovering who is infected and who they might have come into contact with. This has to be done quickly, so the people an infected person had contact with, can be found and informed to isolate, before they themselves spread the virus further. Some countries used this early on in the pandemic (Singapore and South Korea, have successfully used it to contain their outbreaks, while Germany, which has a far lower case and death rate than the UK, has also worked hard on contact tracing.) Others are hoping to implement contact tracing as a means of easing social distancing or coming out of lockdown. To do this public health agencies will have to start aggressively contact tracing and at a much higher level than they were a few months ago. The UK started using contact tracing then stopped, they are now looking to restart it. A plausible way of doing this is to make use of the fact that a lot of people carry a mobile phone, so apps that can help are being developed and used. There are biological factors that need to be taken into account (reliable, accessible testing in the first place) but also logistical, practical and security issues… who are we giving our data to? And what are they doing with it? Could it be used to restrict my freedom in ways other than just managing the spread of the virus? Timandra Harkness author of Big Data, Does Size Matter? and Fellow of the Royal Statistical Society, and a member of their working group on Data Ethics helps answer these questions. Finally, a small bit of good that’s come out of another dark time in our recent history. Atomic bomb tests during the Cold War. The nuclear fallout, doubled the amount of an isotope called carbon-14 in the atmosphere. And that has turned out to be very useful for scientists working on a crucial conservation effort – to age and safeguard the world’s largest fish - the Whale Shark. Presenter - Gareth Mitchell Producer - Fiona Roberts