There are currently two key methods of calculating COVID-19 positivity in use for Florida. They yield far different values for this important metric and the results of this disconnect could be catastrophic.
Background
In a September 28, 2020 NBC Miami news article, Dr. Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases, called Florida’s decision to fully reopen bars and restaurants ‘Very Concerning.’ The article goes on to state that:
Florida has been one of the states hardest hit by the coronavirus pandemic. According to a seven-day count by John Hopkins University, the state’s positivity rate is higher than 10 percent. However, as of Sunday, Florida’s Department of Health reports that the state’s positivity rate is around 4 percent.
NBC Miami
The World Health Organization recommends that positivity rates be at 5 percent before businesses reopen.”
There is a big difference between 10% and 4%, so we decided to try to calculate Florida’s positivity ourselves using both methods.
Positivity Definition and Calculation
COVID-19 positivity is derived by dividing the number of COVID-19 positive tests by the total number of tests administered. This looks simple enough but a lack of a national definition regarding the details of the calculation has led to a number of different algorithms in use.
The following spreadsheet reflects the 10% and 4% positivity results quoted in the Background section of this article. Both organizations refer to positive tests and total tests differently. Positive Increase and Number of Cases Per Day refer to positive tests; whereas Total Test Result Increase and Number of Florida Residents Tested Per Day refer to total tests.
The Atlantic Magazine COVID Tracking Project provides numerous COVID-19 statistics on US states and territories on a daily basis and is used by organizations such as major media outlets, Johns Hopkins University Dashboard and The White House Corona Virus Task Force. Raw data for the COVID Tracking Project is provided by states and territories. Thus, the Florida Department of Health provides raw data on Florida testing and other activities to The COVID Tracking Project.
The Florida Department of Health also calculates a wealth of statistics focusing on Florida.
Positivity Differences
Notice in the above spreadsheet that the number of positive tests each day is rather consistent between the two methods and the big difference is in the way total tests are calculated. Both methods are using the same raw data provided by the Florida Department of Health, but are calculating total tests differently; thus, leading to different positivity values. For the BocaFirst COVID Tracking project, we’ve observed the changes in the definition as the FDOH evolved the data it publishes. The Atlantic puts it this way:
Florida reports testing data in ways that make it difficult to calculate percent positivity—a metric that the CDC uses to refer to the percentage of COVID-19 tests that come back positive, out of all tests performed. Florida does their own quite specific calculations for percent-positive, some of which can’t be replicated by the public, because the state doesn’t report the numbers it uses to derive them.
The Atlantic COVID Tracking Project
Why This Matters
Florida COVID-19 positivity statistics are used to drive important pandemic-related decisions. For example, experts outside of Florida, such as Dr. Fauci, are looking at Florida’s 10% positivity and feel that COVID-19 community spread is still occurring in Florida. Florida officials, such as Governor Ron DeSantis, on the other hand, are looking at Florida’s 4% positivity and reopening up the state from the earlier lockdown. If the 10% positivity is correct and the 4% wrong, community spread could accelerate COVID-19 cases, hospitalizations and deaths leading to a return to restrictions. If the 4% is correct and the 10% wrong, Florida is being unfairly penalized for a high rate of COVID-19 infections.
In addition to Dr. Fauci, New York, New Jersey and Connecticut are using the method that calculates Florida’s positivity at 10% and are requiring people traveling from Florida to quarantine for 14 days upon entering their states.
Having two sets of books regarding Florida’s COVID-19 positivity leads to confusion and potentially dangerous decisions. We reached out to the Florida Department of Health for an explanation of the factors and rules that are involved in their positivity calculation, but they haven’t responded to our request.
