R – its only a data point.

So there is a LOT of panic and fear around this weekend. Again it is important to stand back and let the heads cool. NPHET have warned that “the R-number, or the reproductive rate of the virus, has increased above 1 to potentially as high as 1.8” and Bad Things might happen. Well… maybe

Lets have a think about that shall we. The R here is the reproductive rate of the virus. It essentially tells us how many new cases can emerge from each case. So, above 1 suggests that the virus caseload will rise, below, it will shrink. Right? Maybe. There is a very good article here which looks at the totemc figure https://www.nature.com/articles/d41586-020-02009-w. Three things need to be understood.

First it is an estimate. Like any other estimate it is GIGO – garbage in garbage out. A key parameter is susceptibility. And that we simply dont know. So, its a good as any estimate but not a natural law. And the estimates from the NPHET (date of 9/July) vary WILDLY.

Second, and crucuially here, R can spike up and down when cases are low. If you have 1 case and they infect two others that gives an R=2. If you have 20 cases and they infect 10 you have an R=0.5. We have low new case numbers here so sure as eggs are eggs R will spike. This is more pronounced when you realise also that it is an average. An R for Ireland is an average of R for Leitrim, Louth, Limerick and so on. We saw this in Germany recently

Third, extrapolation of future case dynamics from a particular R estimate is shoddy science. We are, albeit spottily, adopting widespread mask usage. We have sorta kinda internalised the need to socially distance and be hand/cough/sneeze hygenic. Testing and tracing is better than it was, and so on. We are much better prepared for a resurgance than we were for an emergence. So blindly extrapolating R > 1 means Apocolaypse is bad science.

So – R is a datapoint. Just one. Not a mystical determination of our future.

1 thought on “R – its only a data point.

  1. Pingback: Academics (covid) waving at the media… | Brian M. Lucey

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