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expert reaction to latest R number and growth rates, published by the government

The government have released the latest estimates for the COVID-19 R value and growth rates.


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

“These revisions of the ranges for R and the growth rate are more good news, on top of the good news from the ONS Infection Survey earlier today.  But that doesn’t mean we can take the foot off the brake yet.

“The range for R for the whole UK is now 0.7 to 0.9.  Last week’s range was 0.7 to 1.0.  The change doesn’t mean that R has fallen for certain, but SAGE and the Government are now more confident that R is definitely below 1.0.  That corresponds to a falling number of cases, as long as R stays below 1.  The R range is entirely below 1 for England on its own (at 0.7 to 0.9), and for each of the English regions (and that was not true for every region in last week’s figures).  The latest R ranges or estimates provided by the devolved administrations in Scotland, Wales and Northern Ireland are below 1 too.

“The growth rate range for the UK is unchanged from last week, at -5% to -2%.  A negative growth rate is actually a rate of decrease.  So a growth rate of -2% means that the number of new infections tomorrow will be 2% less than the number today.  If the decline continued at that rate for some time, the daily number of new infections would halve in around 5 weeks.  If the growth rate is -5%, and that continued, the daily number of new infections would halve in around 2 weeks.

“Last week, the growth rate range for just one of the English regions (North East and Yorkshire) had 0 as its upper end, meaning that SAGE were not entirely confident that infections were falling there.  But this week, the ranges for every region include only negative numbers, indicating confidence that infections are falling in all the regions.  That includes the South West, which was the only region where ONS estimated that infections might not be falling, in their Infection Survey bulletin today.  A small lack of agreement on something like this isn’t serious; the two sets of estimates are based on different data and have different timescales.  And it is quite a small difference anyway – ONS weren’t saying that infections in the South West were rising, only that the previous fall looked to be levelling off.  So it doesn’t concern me much, except as a reminder that we have to keep a firm eye on all this.”



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



Declared interests

Prof Kevin McConway: “I am a Trustee of the SMC and a member of its Advisory Committee.  I am also a member of the Public Data Advisory Group, which provides expert advice to the Cabinet Office on aspects of public understanding of data during the pandemic.  My quote above is in my capacity as an independent professional statistician.”

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