The SARS-CoV-2 reproduction number or ‘R’ number is a key figure that has been communicated throughout the pandemic in many countries, as it is an important way for policy-makers and the public to understand the current trajectory of infections. In the UK, for example, the consensus on the current value for R, based on modelling by several independent scientific groups, was issued in papers to the UK’s Scientific Advisory Group for Emergencies (SAGE) on a frequent basis during the pandemic, and subsequently to the Government Office for Science for public release.
As the pandemic has progressed, there have been changes in the extent to which SAGE themselves communicated uncertainty linguistically (Baker et al., 2022) as well as in the format of communication of uncertainties around the current R consensus value (epistemic uncertainties) in various SAGE related minutes. For example, both verbal and graphical formats (including graphs and tables) have been used to illustrate the degree of uncertainty, including consensus, on the R number, see Figure 1.
In line with advice in SAGE’s terms of reference (Cabinet Office, 2012; Baker et al., 2022), these formats generally communicate both ‘direct’ and ‘indirect’ uncertainties, as defined by van der Bles et al. (van der Bles et al., 2019). The direct uncertainty is the uncertainty about the estimate itself, often communicated in the form of a range or confidence interval. The indirect uncertainty is the deeper uncertainty about that estimate and range, in the form of some expressions or illustrations of the underlying quality of the evidence (such as disagreement between different models).
Little is known about how these different formats are perceived and integrated into decision making by the audiences receiving them, and yet individuals and policy-makers rely on these official estimates of R to make important and potentially life-changing decisions.
Empirical research has the potential to help guide future communicators of COVID-19 statistics, as well as other important and epistemically uncertain numbers.
a)
“ … SPI-M-O’s consensus view is that Rt in the community is well below 1 and likely significantly lower than the overall Rt in the population. The likely range is 0.5-0.9. We have independent data sources that informs our estimates of Rt in the community.”
b)
Figure 1: Three formats of communication of the uncertainty around R, the reproduction number, of COVID-19 from official government sources in the UK: a) Extract from verbal communication of the uncertainties around R in different subpopulations in the UK (community, hospitals and care homes)(SPI-M-O, 2020b) b) Graph showing the individual modelling estimates and consensus range for the UK as a whole (SPI-M-O, 2020a), c) Table showing the individual modelling estimates for different regions of the UK (SPI-M-O, 2020b).