A groundbreaking survey of Facebook users suggests that around 1% of Britons are showing symptoms for Covid-19 at any given time, with the proportion in Scotland rising as high as 3.5% over the last week. The findings are part of Facebook’s Covid-19 symptom survey, a global effort on the part of the company to use its enormous user base to track the spread of the virus. Since its launch in April, around 120,000 people in the UK have taken part in the survey, registering the presence or absence of Covid-19 symptoms by following a prompt from the social network. Globally, there have been more than 10m responses, the company said. The survey is being run in collaboration with statisticians at the University of Maryland, who worked with Facebook’s Data for Good team to build a publicly available map and dashboard visualising the international results. “By fielding questions that are comparable globally the UK is benefiting from additional data that will be even more valuable going forward as we jointly examine the conditions for reopening in different countries under different scenarios,” said Dr Frauke Kreuter, the director of the university’s joint programme in survey methodology. The symptom survey differs from a number of others in its selection process. Many large-scale symptom surveys require users to opt-in to the survey, by proactively downloading an app or visiting a website. That risks biasing the results, if certain demographics are more likely to volunteer themselves, or if people proactively join the survey when they begin experiencing symptoms. “Survey methodologists and statisticians at UMD value particularly the fact that people cannot self-select into the respondent pool, Kreuter said. “Unlike surveys done via specific apps or websites designed to collect symptom data, the recruitment through the Facebook platform allows us to reach everyone who is using Facebook, and then randomly select within those users.” For the UK at large, the symptom tracker shows a slow but steady reduction in the number of people reporting Covid symptoms, from slightly over 1% at the beginning of May to slightly under 1% now. Within the nations of the UK, the data is noisier for smaller nations, with Scotland reporting zero symptoms some days, and as high as 4% other days – a sign that the programme still has work to do to improve the quality of the data it collects. As well as the surveys, Facebook also analysed location data from its ubiquitous surveillance of its own users to show the extent to which Brits are changing their behaviour as the requirements to stay at home are lifted. At the beginning of April, 46% of English people were staying in place, Facebook’s tracking revealed, while that figure has dropped by a quarter, to 36.9%, in the latest data. Similar declines were seen in Northern Ireland, Wales and Scotland. In this, Facebook’s data is similar to that gathered by Google and Apple through their mapping programmes, released much earlier in the Covid crisis. All three companies have seen mobility rise significantly from the lockdown lows, with some countries, including the US and Germany, returning to normality, as measured by requests for directions.