As of yesterday, 4/8/20, this site reported 427,460 cases of COVID-19 in the US.
Let’s do some math. On 3/16 there were 4226 cases. That’s 23 days of growth and we see a ten-fold increase. When something grows by a factor of ten (that is, 10x) we say the increase is “one order of magnitude.”
The natural logarithm of 4226 (ln 4226) is roughly 8.35 and ln 427460 is roughly 12.97 and that difference (12.97 – 8.35) is 4.62.
Using the same math as before, I divide 4.62 by the 23 days of growth and get 0.20 which is 20% growth. We’d love 20% growth on our investments, right? That’s still a high rate. But it has come down from the 30% we got previously. Remember we had seen that figure drop to 27%.
We now take ln 2 and divide by 0.20 to get the doubling time. The result is 3.47 or about 3-1/2 days. That beats the 2.56 we got last time! Remember that I’m just running these numbers for fun, they are not meant to be a serious analysis.
According to this site the doubling time in the US is currently 8 days. That’s good news. We continue to see the rate of growth of new infections dropping.
One caveat: testing, as we know, is woefully inadequate. We won’t get a real handle on the numbers of infected people without widespread testing. There could be a lot of asymptomatic carriers and if we can’t test enough people then we can’t know for sure. But so far we have seen that aggressive social distancing measures appear to make a big difference. So, keep up the good work, people!