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What's percent positive? How to read COVID-19 data

There is a lot of coronavirus data but one number is really important, the percent of positive cases. It gives us insight into how a community is handling reopening.

FLORIDA, USA — To bring you the latest information on the coronavirus we comb through a lot of data to make sure we’re giving you context. But when it comes to reopening, there is a key piece of data experts say we should be watching -- the percent of positive cases.

Going through COVID-19 reports can feel like you are swimming through a sea of numbers.

We look at things like new positive cases, average ages, age groups, residents, non-residents, total cases and the death rates.

You can get lost in the numbers if you don't know what to look for.

There's one piece of information though experts say we should be thinking about every day. The percent of positive cases.

That helps us understand if we are doing enough testing and how an overall community is responding to the pandemic.

If we see a consistent rise in the percent of positive cases than we know more people on average are being infected. You can’t just take the percent positive at face value, however. 

According to Dr. Jill Roberts with the USF College of Public Health, it’s more complex than that.

"The problem with percent positive is it varies with how much testing we do," Dr. Roberts said. "You can not compare percent positive from one day to the next. Unless the number of tests is the same."

That means you can’t compare a day with high testing to a day with low testing. That won’t give you an accurate picture of how the virus is spreading.

RELATED: Florida coronavirus cases, deaths, hospitalizations, recoveries

A common misconception about the percent of positive cases is that as we do more testing the number will automatically go up. Doctor Juan Dumois from Johns Hopkins All Children’s Hospital said that is not true.

"That is not true at all," said Dr. Dumois. "The raising of the percent positive in a community means that there is more virus infecting more people."

Think about it like apples. If we looked at 10 apples and found worms in six, 60 percent infected. If we looked at 50 apples though and still only found six with worms, that number changes to 12 percent. If it was 100 apples and still only six had worms, six percent infected.

So to really know what the percent of positive cases is we have to be doing as much testing as possible.

RELATED: With another day of 13,000 positive COVID-19 cases announced in Florida, the Governor believes cases are stable

RELATED: Why are we reopening schools in Florida?

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