After a number of conversations yesterday with various people about why there is such a divergence in individual responses to the call for social distancing, I went to my spreadsheet. As a trained financial economist, that’s what we do. We make a model. As it turns out, this is a pretty simple model. The general rule of thumb is that we can expect the number of cases to double every two days. So, the number of cases grows by 50% every day.
When you start to map those numbers out over the next 30-45 days, you start to understand why this is such a big deal. Today doesn’t look that bad. Neither does tomorrow. In fact, it could take a while before most of us even know somebody who is sick. Unfortunately, by the time there are enough people sick that we take notice, it is too late. The impact of doubling every two days is about to get very ugly.
At first glance, a 50% daily growth rate (the green line) continuing over the next three weeks doesn’t seem terrible. When you get to Day 21, however, the number of cases can shoot up from 500,000 to 3,000,000. Essentially, that is the point where every single person in the state of Mississippi has tested positive for COVID-19. On the other hand, the long-term impact of slowing the growth rate just a little has enormously important consequences. If we slow the growth rate from 50% daily growth to 40% daily growth (the blue line), the number of cases in the state of Mississippi stays below 500,000 over the next 30 days.
Let’s take a closer look at the next two weeks.
The growth and number of forecasted cases remains small over the next week. People are easily lulled into a sense that this is much ado about nothing. It’s going to take another 7-10 days before the growth in cases reported becomes noticeable by the public. It could take another 2-3 weeks before you even know somebody who tested positive for COVID-19. On the other hand, you also see how meaningful social distancing over the next two weeks can drastically reduce the number of cases in the state. This is illustrated by the difference between the green line 50% daily growth) and the yellow line (30% daily growth).
If you want to see a closer look at the actual numerical forecasts over the next 14 days, I have included that. Currently, I am only using 3 days of data in the model along with the estimated growth rates being given to us by the government entities. If Mississippi experiences a daily growth rate of 40%-50%, this accurately predicted the 50 cases reported as of today, March 19. It predicts a total of 70 confirmed cases tomorrow. Come back tomorrow to get an update.
I am not a medical doctor, a healthcare specialist, biologist, or public health professional. I am a trained financial economist building an economist growth model and explaining the impact of personal and policy outcomes on that model. The base data and general growth rates come from the following sources: