COVID-19 Numerology

Warning: Discussing death is difficult, and if you feel you will be offended by this discussion, please don’t read any further.

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Life is very pleasant for me and my wife in this ‘stay at home’ world, but I find myself permanently anxious and neurotically focused on ‘the numbers’: trying to understand them and use them to foresee what’s coming next.

I had thought naively that the ‘lock down’, which started on Day 81 of the year, would be completely effective, and that new cases of COVID-19 would begin to decline. But as the data below shows, that doesn’t seem to have happened.

Slide1

The number of new cases has stopped rising – but new cases are still occurring at around 4500 ± 500 cases per day.

As I understand the data, and the way in which testing is done, these are mainly people entering hospital. People who have probably been ill at home for some time, but their symptoms have now become serious enough for them to come to hospital.

But even so, some of those people will have been infected after Day 81.

Relating New Cases to Deaths

Some fraction of the people entering hospital will die a few days later.

I have looked at the UK data to try to understand how many people would die – the fractional mortality – and the delay.

To do this I took the ‘new cases‘ data and:

  • Applied a delay to the data that moves it to the right on the graph
  • Adjusted the fractional mortality to try to match the statistic for daily deaths. This moves it downwards on the graph.

Slide2

I found a reasonable match to the data for a delay of 7 days and a fractional mortality of 25%. i.e. the data seem to imply that 1 in 4 people being admitted to hospital as a new case will die, on average just 7 days later.

Slide3

Is this right?

Well obviously I don’t know if this is right or not.

I had expected a much lower mortality for people entering hospital – perhaps 1 in 10. On the graph above this would push the dotted black curve downwards.

But if that were so, then in order to match the ‘daily deaths’ data, the time to death would have to be very short, and in fact the curve doesn’t match the data well.

I found that reasonable matches could be obtained with:

  • mortality of 30%  and a time until death of around 9 days,
  • mortality of 20%  and a time until death of around 5 days,

But the best match (by eye) seemed to be with a mortality of 25%  and a time until death of around 7 days,

Discussion

I was shocked and saddened by this result. I hope I have missed something out or misinterpreted the data. Perhaps the mortality or time until death have improved throughout the last few weeks.

A mortality rate of 25% has been reported in the ‘worst hit’ hospitals, but I assumed this was exceptional. Also, the time until death seemed much faster than I had expected.

One additional feature of this analysis is that – if correct – it predicts the number of daily deaths for the next 7 days. And the prediction is disappointing.

The analysis indicates that the number of daily deaths in the next 7 days is unlikely to fall because these deaths correspond to people who have already been admitted to hospital.

Link to Excel Spreadsheet: Modelling Death Delay and Mortality

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As I mentioned, discussing death is difficult, and if you have been offended by this discussion, I apologise. The reason I have written this is that I feel it is important that we all try understand what is happening.

 

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5 Responses to “COVID-19 Numerology”

  1. paulmartin42 Says:

    I wonder if we are instinctively drawn to curves that peak; political policy has been driven by flattening of such since they are easy to visualise. ( In the same way the outliers are notorious of late because such make good TV. ) My worry is that “Test Test Test”, another media meme as spoofed by Harry Hill’s “Bring on the wall”, will exhaust its credibility because we don’t understand the underlying problems involved, either.

    I think Feynman was thinking along these lines in his 1976 University of Auckland lecture which I watched a while back and then again most recently. The Q&A at the end exemplifies that the audience did get (some of) it. I don’t doubt that our education system will be improved by the reflection that the extended break will provide. I for one have learnt that the fact that 10 pence worth of highly sprung chemicals can bring society to its knees explains why we need a sense of humour.

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