March 9th: The math of epidemics

The problem with epidemics is that our brains were not "wired" for exponential mathematics. There is a story about an ancient king who was bargaining with a merchant about a payment in the form of rice. Finally the merchant asked for a chess board. He said: "all I want is a grain of rice on the first square, 2 on the second square, 4 on the third ...and so on, doubling the amount on each square." "That's all?" Said the king... "granted!" Unfortunately for him it turned out that there was not enough rice in the entire kingdom to pay the merchant!
So what's the lesson? The lesson is that if every infected person infects 2 you have the same mathematics... and the time to stop the process is when the numbers are still so small that the problem is not yet obvious, So effective action will always seem premature and alarmistic. Any action needs to be proportional NOT to the present numbers but the numbers to be expected in a week or month... and that's not a function of irrational fear. It's a function of mathematics. Sorry about that!

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