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How to read COVID-19 numbers

How to make sense of COVID-19 numbers

PHOENIX — Beyond the daily count of cases and death tolls, the Arizona Department of Health Services releases a lot of data about the coronavirus pandemic.

Here's how to make sense of it.

We asked University of Arizona Medical School's Dr. Shad Marvasti to help explain the data we're seeing. 

For starters, the number of cases in Arizona keeps going up, while the number of deaths appears to be going down. 

But Dr. Shad said that might not mean the virus is getting less deadly. 

“We’re trending way up, that’s the problem," Dr. Shad said. 

Dr. Shad said death reporting is usually delayed by a few days, so the drop in deaths could go away in the next week. 

"So we’re not going to see it for a few weeks out because usually people die after a fight...you know, 2, 3, 4 weeks out," he said. 

Dr. Shad said hospitals are getting better at keeping people alive longer, though those same patients may still end up dying. 

Also affecting the death rate is the demographics of the sick. 

COVID-19 is deadliest to people over 65. 

But the state number show by far the biggest number of cases is in the under-44 age group. 

“That’s reflective of all the folks you know hanging out inside bars and other places where it’s poor ventilation indoors without any masks," he said. 

The state also releases numbers showing the numbers of COVID-19 tests being done, as well as how many of them are positive. 

Dr. Shad said that last number can be very telling.

If the number of cases was increasing simply because the number of tests was increasing, then the percentage of positive tests should stay about the same. 

But it's not.

“When you see a higher rate of percent positive," Dr. Shad said, "then you know it’s not just because you’re testing more.”

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