South Africa: COVID-19 - Simple Statistical Predictions for South Africa

Coronavirus (COVID-19) disease graphic.

There is a saying that you never want to be on the wrong side of an exponential, and nowhere is this more true than during a pandemic. While I'm not a virologist or epidemiologist, there is a great deal of value in understanding the simple 'back of the envelope' statistics behind the coronavirus outbreak and the implications for South Africa.

During a viral outbreak, the total number of infections follows what is known as a logistic function, an S-shaped curve characterised initially by exponential growth and then flattening out as either the outbreak is brought under control through external interventions such as quarantine, or the virus spreads through so much of the population that there are no new host possibilities. China's Hubei province - in which the city of Wuhan was the initial source of the viral outbreak - illustrates an almost perfect logistic function. The virus runs rampant through the population (the exponential element of the function) before severe quarantine measures bring it under control.

Unlike pure exponential functions where the number of infected could continue to grow forever, logistic functions have a changing slope, calculated by dividing the total number of cases today by the total number of...

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