State and federal health officials both use two key metrics — test positivity and the rate of new cases per 100,000 people — to calculate COVID-19 transmission. But there are some key differences in the details between the numbers used by the Centers for Disease Control and Prevention and those used by New Hampshire's Department of Health and Human Services.
While the CDC looks at the rate of new cases per 100,000 people over the last seven days, New Hampshire looks at the last 14 days. The CDC also doesn't include antigen tests in its positivity rates when calculating risk levels, but New Hampshire does include antigen tests in its positivity calculations. And while the CDC keeps all county data together, New Hampshire separates out COVID-19 data from its two largest cities (Manchester and Nashua) from the rest of Hillsborough County.