Government target of 200,000 Covid-19 tests 'meaningless'
The government’s target of hitting 200,000 Covid-19 daily tests by Monday has been described as “meaningless” by senior scientists, who say that the published data on testing does not adhere to the basic rules of statistics.
Experts told the Guardian the published daily testing figures appeared “almost designed to confuse” and made it impossible to judge whether current levels of testing are adequate to support the track, trace and isolate programme that is said to be essential for easing lockdown.
Concerns included the failure, for the past five days, to release data on how many people have been tested, the reported double-counting of multiple swabs (nose and saliva) from the same individuals, and the inclusion of tests that have been mailed out to homes and satellite labs, but not returned, in the daily tally.
Prof John Ashton, a former regional director of public health and regional medical officer for the north-west of England, described the published statistics as “all over the place”.
“It’s very difficult, even for someone like me whose living has centred on numbers, to know exactly what is going on. We don’t know how many people have been tested. We don’t know how many tests have been satisfactory. There’s a real problem of transparency and trust,” he added.
Prof Sheila Bird, formerly of the Medical Research Council’s biostatistics unit at the University of Cambridge, described the reported double-counting of tens of thousands of swabs where saliva and nasal samples taken from the same patient were counted as two tests, as “pretty incredible stuff”.
“Considering the swab of the left nostril and the right nostril of the same person as two tests would be most unfortunate,” she said. “If there are those issues in the hinterland, they need to come to the fore and be explained.” “Good statistical practice says that you must first define what you’re counting,” she added. “That would be a good start.”
On 6 May, Boris Johnson said that “the ambition clearly is to get up to 200,000 [tests] a day by the end of this month”.
However, on 26 May, 117,000 daily tests were performed or mailed out and no total figure was available for how many people were tested. And there are unexplained gaps in the published daily figures that raise further questions about the true extent to which testing capacity has been scaled up in the past month.
Since testing was expanded to include home testing and tests mailed out to satellite sites, a gulf has opened between the number of pillar 2 tests carried out each day and the number of people tested – by 21 May the gap had reached more than 500,000 tests (45% of the total).
The Department of Health said this is due to retests and because some tests mailed out have not yet been returned or used. It declined to say what proportion of tests have left the system and not come back.
For the past five days, no figures have been provided for the number of people tested in pillar 2 – or overall – and the latest bulletin states reporting of these figures have been temporarily paused “to ensure consistent reporting across all pillars”.
David King, former government chief scientist and chair of the independent Sage committee, said the lack of transparency over figures was “very
concerning” and that his advisory committee had reached a point of “sheer frustration” over the handling of testing. “The real value of testing in the middle of a pandemic is to couple testing with the track and isolation that follows,” he said. “We’re opening up from the lockdown without having the test, track and trace process fully operative. It should’ve been tested for a week beforehand and showing good results.”
“We have to ask what’s the point of aiming for 200,000 if we haven’t even got up to 100,000 with track and trace?” he added. “We’re much more likely to go into a second peak in the outbreak unless we have test, trace, isolate fully in place.”