David Norgrove states that the aim of government testing data 'seems to be to show the largest possible number of tests, even at the expense of understanding'
In a letter, David Norgrove, Chair of the UK Statistics Authority, responds to Secretary of State for Health and Care Matt Hancock regarding the government’s COVID-19 testing data. In his key points, he thanks Matt Hancock for his letter but is 'afraid though that the figures are still far from complete and comprehensible'. He outlines two main purposes for statistics on testing: to help us understand the epidemic and to help manage the test programme. 'The way the data are analysed and presented currently gives them limited value for the first purpose. The aim seems to be to show the largest possible number of tests, even at the expense of understanding. It is also hard to believe the statistics work to support the testing programme itself. The statistics and analysis serve neither purpose well.' He highlights 'a few issues' in the data as currently presented, including:
- The headline total adds together tests carried out with tests posted out: 'This distinction is too often elided during the presentation at the daily press conference, where the relevant figure may misleadingly be described simply as the number of tests carried out. There are no data on how many of the tests posted out are in fact then successfully completed.'
- The notes to the daily slides rightly say that some people may be tested more than once and it has been widely reported that swabs carried out simultaneously on a single patient are counted as multiple tests. But it is not clear from the published data how often that is the case. Figures for the overall number of people being tested have previously been published but are not available in the published time series.
- The top summary presents the number of positive results from diagnostic tests alongside the total number of tests across all pillars, which gives an artificially low impression of the proportion of tests returning a positive diagnosis.
- 'More generally the testing figures are presented in a way that is difficult to understand. Many of the key numbers make little sense without recourse to the technical notes which are themselves sometimes hard to follow.'
David Norgrove says the testing statistics fall 'well short' of the expectations of the Code of Practice for Statistics. 'It is not surprising that given their inadequacy data on testing are so widely criticised and often mistrusted.' He welcomes the Department of Health and Social Care's willingness to work with colleagues from the Office for Statistics Regulation. He also says it would be useful to develop a published timetable for the changes needed and for the development of metrics for test and trace.
UK Statistics Authority correspondence