Sunday, December 20, 2020

Coronavirus 45 Tragedy of Commons

Some sums in the head. Maybe one in a hundred people out there have covid. You'd have to be out and about, shopping, travelling or whatever, for quite a while before meeting a hundred people. But say you do meet someone who is infectious. If the reproduction number, R, is between 1 and 2, that infectious person will, on average, infect one or maybe two others, but they may, like you, have been out and about and met a hundred people, not just you. And you are sensible, you wear a mask, you keep your distance. You wonder what the chance of catching the virus will be if you go out and about. You know you have to multiply probabilities and though you don't have accurate numbers you know the probability of catching the thing if you go out is pretty low. One in thousands. A lower probability of harm than other things you do, skiing, horse-riding, smoking cannabis. Yes, on a personal level, going out is safe enough.

But you are thinking about yourself, not society. A one in a thousand chance sounds low but if one in a thousand people die from covid in a population of 67 million then 67,000 die. Tonight's government figure for UK death is 67,401. (The excess death number is about 80k and the second wave has a long way to go yet.)

There's another thing, if you do catch it, and with R>1, it doesn't stop there. You pass it on to others and they... until hundreds of thousands die. That's the inevitable outcome if R stays above 1. The arithmetic demands it.

And this is the new variant of the Tragedy of the Commons. Your behaviour may feel like a personal advantage, you get to go out and about, at least for a while, but when you, and everybody else who makes a similar judgement, behaves this way, disaster results. For everybody.

When deciding what to do we sensibly consider the personal short term risks and benefits. Big mistake. It is the commons that counts, the risks to society as a whole if everyone acts as you wish to.

Picture credit: Royal College of General Practitioners.


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