Monday, May 11, 2020
Dr. Thode Analysis: Northeast Could Be Locked Down Until July!
Dr. Steve Thode, the retired Director of Real Estate Studies at Lehigh University, has been crunching the daily numbers from the Covid-19 crisis. He has a disturbing prediction. Based on his analysis, and assuming that Governor Tom Wolf insists on following his own formula, we will be locked down until sometime in July. (July 5-17).
All I can say is I sure hope he's wrong. Based on the rumblings in other counties, I suspect Wolf will have to open sooner.
Dr. Thode's Forecast Methodology
I started tracking COVID-19 daily new case data for all 10 counties in the Northeast Region beginning on March 30, 2020. Those counties are: Lehigh; Northampton; Luzerne; Lackawanna; Monroe; Carbon; Pike; Wayne; Susquehanna; and, Wyoming. I use the daily case data for each county as reported by the Pennsylvania Department of Health.
When Governor Wolf announced the regional requirement to go to “Yellow” as 50 cases per 100,000 residents for a 14-day consecutive period, I calculated that statistic using 2019 estimated population statistics for each of the 10 counties and the daily new case data for each of the 10 counties.
The 2019 estimated total population for the 10 counties is approximately 1,612,000. That translates to a 14-day COVID-19 new case rate of 806 total new cases.
The 14-day new case rate for the 10 counties peaked at 5,216 on April 15. It has declined substantially since then. For example, by April 29 (14 days later) the 14-day new case rate had dropped to 2,926 for the 10 counties.
I developed my forecast for going to “Yellow” by calculating the geometric average percentage drop in new cases for each 14-day period beginning with the period ending April 29. That captures the total number of new cases from April 16-29. April 16 was the first day the 14-day case rate began dropping consistently.
For example, on April 29, the 14-day case rate had dropped from 5,216 on April 15 to 2,926. That’s a drop of 43.90% over 14 days. That translates to a geometric average drop of 2.63% per day over the period from April 15 to April 29.
From this, I developed two estimates of when the Northeast Region would see its 14-day new cases drop to 806 – the criterion for going to “Yellow.” Both estimates use the daily geometric average percentage drop for the 10 most recent 14-day periods. This is what is known as an exponential decay function.
The first forecast, which I call the “Unweighted” forecast, simply averages the daily geometric percentage drop for the last 10 days, and projects future 14-day case rates based on that average.
The second forecast, which I call the “Weighted” forecast, weights the daily geometric percentage drop from the most recent days (of the last 10 days) more than the earlier days (of the last 10 days). Why? Because the percentage drop has been declining. For example, on May 10, the 14-day case rate was 2,396. 14 days earlier (April 26), the case rate was 3,175. That’s a drop of 24.94% (or a geometric average of 1.58% per day). So, the case rate continues to decline, but more slowly on a percentage basis.
Dr. Thode's Data Caveats
Any forecast is only as good as the data upon which it relies. There are at least two issues with daily reporting of new cases in the 10 county Northeast Region. Some reports are clearly in error. Susquehanna County has reported a negative number of new cases on a couple days. I simply marked those as “0” in my data set.
The more difficult problem is relying on the daily cases reported by each county as actually being the number of new cases from the previous day (or previous 24 hours). There appear to be some “data dumps” in the reporting. For example, on April 28, Northampton County reported 136 new cases – more than the three previous days combined. On May 10, Lehigh County reported more new cases (72) than it had on any day since April 30. Likewise, on May 10, Luzerne County reported more new cases (60) than it had reported on any day since April 14. There is nothing I can do about that.