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What is percent positivity and how is it used?

Percent positivity is the percentage of all COVID-19 diagnostic tests that are positive on a given day. This is metric indicates whether enough tests are being done to detect most new cases. If enough diagnostic testing is being conducted each day, a low percent positivity (less than 3%) over a period of time can give us confidence that the spread of disease is under control.

Epidemiologists watch the percent positivity over weeks within an area since the number can fluctuate daily based on the number of tests performed.

  • Where can I find percent positivity data? Percent positivity is posted daily on the "Diagnostic Testing" tab at Michigan.gov/Coronavirus
  • How is percent positivity calculated? Percent positivity is the number of positive diagnostic tests in a given day divided by the total number of diagnostic tests performed that day.
    • Number of positive tests / Total number of tests performed in the same day = Percent positivity
    • Percent positivity data may include results from people who have tested positive more than one time, since that information is helpful in deciding if there are enough tests being performed. However, each individual is only included in the confirmed case count once.
  • Do other states follow percent positivity calculations? Yes! Percent positivity is important to epidemiologists across the country and worldwide. You can find national numbers for percent positivity on the CDC data tracker.