“ In the mid-19th century, Dr. William Farr made the observation that epidemic events rise and fall in a roughly symmetrical pattern that can be approximated b

“ In the mid-19th century, Dr. William Farr made the observation that epidemic events rise and fall in a roughly symmetrical pattern that can be approximated by a bell-shaped curve. ” Yes, he got as Farr as noticing that it’s roughly bell-shaped. But just because it goes up and then down it’s not actually a normal distribution. At the beginning, when no one is immune, infections obviously grow exponentially. But the bell curve, even though it looks similar (sigmoid) doesn’t rise exponentially. So it looks similar, but it’s not. If you observe infections and somehow try to fit a normal distribution, you’ll get widely wrong predictions, especially at the beginning. Farr came up with this in 1840. That’s before Pasteur formulated germ theory as we know it today, so it was probably close enough for its time. Today it’s not.