COVID-19 Interest Group

April 3, 2020 


Arlin‘s Corner  # 1     COVID-19 Interest Group    April 3, 2020


The data, information and estimation of future cases presented below is based on public data and my own personal mathematical analysis of it. It has not been peer reviewed and has not been officially endorsed by the Berkeley Rotary Club. It is a brief summary concentrating on today's Covid19 situation in the Greater Bay Area and Alameda & Contra Costa Counties. If you have any questions, please call me at 510-501-0298. If you are interested in a copy of my Excel spreadsheet for the analysis of GBA or A&CC data, please e-mail me at  [email protected]......Arlin Peters


A summary data table of cumulative confirmed Covid case data as of the evening of April 2nd is shown below this analysis. These are Covid19 cases confirmed by a positive test result, and are the total number as of the date. It is thought that due to the lack of testing especially for mild and moderate cases, the actual number of cases on a particular day is 7 to 10 times the number of confirmed cases.  

The Greater Bay Area (GBA 7 counties w 7.1 million people) has 2886 cases or 406 cases per million (cpm), on the low side of many locations. Alameda and Contra Costa Counties (2.8 million population) has 649 cases or 232 cpm.

 Doubling time (DT) is crucial to understanding the exponential growth of the Covid epidemic. It is calculated based on past data and is the number of days it takes for the number of cases to double. DT is a measure of how well the public is using good hygiene and social behavior to slow the transmission of Covid19 cases. 

 Smaller DT’s are bad because the number of cases doubles in fewer days compared to larger DT’s. A DT of 5 is equivalent to a 15% daily increase of the number of cases. A DT of 7 is equivalent to a 10% daily increase in the number of cases.  A simple way to get the % daily increase is to divide 70 by the DT. Example for a DT of 7, 70/7 = 10%. Exponential growth is similar to compound interest at high daily interest rates!

  DT calculated from data over the past 14 days can be compared to the rolling DT calculated over the last 4 days to see if public transmission rates are decreasing. The GBA DT average over the past 2 weeks was 5.4 days. The current GBA 4 day rolling DT is about 7. Things are getting better, even though it's hard to see in just today's increased number of cases.

 Below the data table is a graph of GBA rolling 4 day DT, so you can see the DT progress over time. We need further progress to get to DT's of 10, 15, even 20+ days! We all need to build on our good hygiene and shelter in place, self-isolation practices, especially since many of us are over 65. 

  With a 7 day DT, I estimate the GBA’s number of cumulative confirmed cases will rise to about 11,500 in two weeks. Improving DT’s over the next two weeks will reduce the number of cases.

 I estimate from the growth of the number of confirmed cases and several assumptions and including the 7x factor for untested cases, that the number of GBA contagious cases on April 2 was 0.34% of the GBA’s 7.1 million population. The risk of transmission is low, but it will increase as the 7 day DT means more infected and contagious people in the future. I estimate that in a week from April 2, 0.6% of the GBA population will be contagious.


Covid Cases  Summary Data 4/2/20 evening  ARP  
      DT is # of days for the # of cases to double
    Covid Confirmed   Long term 2 wk avg  
  Population Confirmed Cases per   Doubling  DT DT over 
  millions Cases million   Time (DT) Trend last 4 days
USA 331 245,646 742        
Calif 40 11,187 280        
GBA 7.1 2,886 406   5.4 increasing ~7
GBA Estimated cumulative cases in 2 weeks = 11,500  w DT=7  
GBA Estimated currently contagious = 0.3% of population  
Alameda & 2.8 649 232   4.8 increasing ~7
Contra Costa Co