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Testing Data

U.S. COVID-19 Test Positivity Data Differs State By State

The Coronavirus Resource Center developed a national standard for comparing positivity rates among U.S. states that used multiple other calculations

May 17, 2021

COVID-19 test positivity rates calculated by the Johns Hopkins Coronavirus Resource Center often differ from the results reported by states across the nation.

The reason: the federal government has not imposed a standardized method for calculating COVID-19 testing data upon the states.

The differences led to many disputes among states as they were setting out-of-state travel policies based on conflicting test positivity calculations. The experts at the Coronavirus Resource Center frequently debated in good faith with state health officials when the website’s calculations resulted in rates higher than what states had calculated.

The Coronavirus Resource Center has described the differences in exhaustive detail on the Testing section of the website.

Among other things, the Pandemic Data Initiative will explore how and whether the United States can go from multiple different calculations to a uniform method informed by the best evidence-based research available.

It is a complicated endeavor. Since the beginning of the pandemic, multiple states have been inconsistent with numerous aspects of testing data. Some states shared their positivity formulas, others did not. Many states shifted from reporting data every day to every week. Others mixed results from PCR and antigen tests, the two main testing methods.

All of these actions created abnormal spikes in positivity rates when trying to apply a uniform standard across the United States as the CRC has done. The Coronavirus Resource Center team decided to devise a uniform method to best serve the public and the media as they sought to view the pandemic through a national lens or compare progress between states.