Estimating R to support policy decisions in the UK
The PSC publishes metrics and methodology to help decision-makers assess whether the government’s “5 tests” for lifting the lockdown are being met.
As the UK’s government and scientific decision-makers consider releasing elements of the COVID-19 lockdown, the government has set “five tests”, three of which relate to quantitative measures of infection rate. These three tests ask:
(1) Have we moved beyond the peak, with a consistent and daily fall in the death rate?
(2) Do we know that the rate of infection is decreasing?
(3) Do we risk a second peak?
In Germany, the government’s approach to these type of decisions is supported by the Robert Koch Institute publishing a daily estimate for “R”, at a national level, helping to provide insight to decision-makers on how fast the infection rate is decreasing and on the size of the near-term risk of a second peak.
In the UK, “R” is referred to as a “critical indicator” informing the questions above, but in spite of this there is as yet no regular publication of estimates of its value, either nationally, regionally or locally. The recommendation of this paper is that the UK should publish quantitative measures that help to provide insight on the three questions above.
This paper, written under the name of 2020 Delivery, illustrates a simple growth index, G, which can be used to illustrate the rate of growth (or shrinkage) in COVID infections. Like R, G has value > 1.0 when infections are growing, and has value < 1.0 when infections are shrinking. The advantage of G over R is that it can be directly and simply calculated from published data, at local, regional and national level.
G can be used to look at three important dimensions of the COVID-19 pandemic in the UK:
- Growth index in the number of COVID infections using G-diagnosis;
- Growth index in the number of COVID hospitalisations using G-hospitalisations;
- Growth index in the number of COVID deaths using G-deaths.
The paper illustrates substantial regional variation in the UK’s growth index in the number of COVID infections as shown by the metric G-diagnosis, which will be important for policy-makers to consider as they take decisions on lifting elements of lockdown. The paper also demonstrates that Germany continues to have a faster rate of decline of the COVID-19 pandemic than does the UK, in spite of the UK’s continuing lockdown.
Author: Russell Cake, Director at The PSC
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