How accurate are the results from self-testing for covid-19 at home?

IN THE UK, essential workers are now among those being sent home testing kits for coronavirus. This involves swabbing the inside of your own nose and the back of your throat, but how useful are the results? Studies from early in the outbreak in China have suggested that swabs taken by healthcare professionals may give a 30 per cent "false negative" rate, where infected people are told they don't have the virus (NEJM, doi.org/ggmzsp; medRxiv, doi.org/dvfr). This has prompted claims that self-testing will give even more false negatives and could raise the risk of infected people spreading the virus. No test is perfect – swabbing technique and analysis errors can lead to inaccurate results.