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expert reaction to latest data from the ONS COVID-19 Infection Survey

The Office for National Statistics (ONS) have released the latest data on COVID-19 from their Infection Survey.

 

Prof Kevin McConway, Emeritus Professor of Applied Statistics, The Open University, said:

“The latest ONS Infection Survey results add the week from 2 to 8 October to the previous picture. The very broad message is much the same gloomy one as in last week’s ONS bulletin. The estimate of the number of people in the whole English community population that would test positive for the virus has continued to increase, with no clear sign that the rate of increase is slowing. The same is true for the estimate of the daily number of new infections. But there are some potentially important details about different regions and age groups, that do show some change from the previous week.

“As always, results from the ONS survey should provide more reliable estimates of these numbers than the figures that come from testing within, for instance, the Test and Trace programme. That’s not because the tests used are any different – the swabs are analysed in the same labs using the same methods – but because the ONS survey uses data from a reasonably representative sample of the community population. They are tested only to provide these estimates, and not because they have asked for a test because they have symptoms, or have been advised to have a test by health professionals.

“Overall, ONS estimate that, in the week ending 8 October, 1 in 160 of the English community population (excluding people who live in communal establishments like care homes or some university halls of residence) would test positive for SARS-CoV-2. Because this estimate comes from a survey, there’s some uncertainty about it, and the data are consistent with a rate between 1 in 150 and 1 in 170. Putting it another way, the central ONS estimate of the number of people who would test positive is 336,500, with a credible interval (plausible range) from 312,200 to 362,000. These are estimates of the numbers who would test positive. At this level of infection, it’s probably the case that the number of false negatives (people who are actually infected but would test negative) considerably outnumber the number of false positives (people who are not infected but would test positive), so that the actual numbers of infected people are likely to be rather higher than those estimates.

“ONS estimate that there were 511 new infections per million people each day, with a credible interval from 415 to 699. In numbers across the English community population, that’s 27,900 new infections each day (with a credible interval from 22,700 to 38,200). As always, these figures are considerably higher than the daily reported ‘new cases’ on the Government dashboard, for which the daily rate (as an average over 7 days) was about 13,000 for England for the week in question. The difference is partly because people without symptoms would be unlikely to be tested under the system that provides these daily figures, so they would not show up as a confirmed case. People with no symptoms are still tested if they are in the ONS survey sample, and some of them will actually be infected and test positive.

“As last week, the differences in rates of positive tests between different regions are very clear, with considerably higher infections rates in the three regions of northern England (North West, North East, Yorkshire & The Humber) than elsewhere. What’s new is that, in two of these regions (North East, Yorkshire & The Humber) there are signs that the increases are levelling off. ONS, rightly in my view, urge caution about interpreting these signs – there’s quite a lot of statistical uncertainty in the numbers, and a levelling off over just one week might not indicate a more permanent slowing, let alone a clear downturn. But at least it’s a spark of light amongst the gloom. In the North West there’s not yet any sign of such a slowing. Indeed, in the regions in the Midlands and South that’s also the case, though the infection rates there remain quite a lot smaller than in the three Northern regions.

“The infection rates are again highest in younger age groups, particularly those aged about 18 to 24. There are signs that infections are increasing more slowly in the 18 to 24 group, though they still seem to be increasing. And there are clearer signs of growth in infections in age groups between 25 and 69 years. So far these indications of growth don’t apply to those aged 70 and over, where the rates are still much lower than for other ages.

“The survey is also now running in all four UK countries. It has not been running for long in Scotland, and no results are yet available. In Northern Ireland there’s more statistical uncertainty than in England, because the number of people tested in the survey is a lot smaller. Therefore trends from one week or fortnight to the next are not clear from these data. In Wales, though infection rates have increased since early September, there’s some evidence for the latest week that the increase is levelling off. However, again because the number of people tested is small compared to England, there’s a lot of statistical uncertainty about that conclusion.”

 

 

https://www.ons.gov.uk/peoplepopulationandcommunity/healthandsocialcare/conditionsanddiseases/bulletins/coronaviruscovid19infectionsurveypilot/16october2020

 

All our previous output on this subject can be seen at this weblink:

www.sciencemediacentre.org/tag/covid-19

 

Declared interests

Prof Kevin McConway: “I am a Trustee of the SMC and a member of the Advisory Committee, but my quote above is in my capacity as a professional statistician.”

None received.

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