Updated Oct. 24, 2020

In the United States, there have been hundreds of thousands of deaths attributed to COVID-19 since the start of the pandemic. But CDC scientists suspect there may be more people who died, either from undiagnosed COVID-19 or from other causes related to the pandemic.

”Pandemics and disasters often cause what we call ‘indirect’ deaths,” says Lauren Rossen, a data scientist with CDC’s National Center for Health Statistics (NCHS). “An example of this is when someone dies of a heart attack or stroke because they were afraid to go to the hospital, or if changes in people’s circumstances lead to increases in suicide or drug overdose. We don’t know what’s really happening until we look at the bigger picture.”

So how do we get this bigger picture? That’s where what researchers call “excess death” data come in. Simply put, excess deaths are the difference between the number of deaths that were expected to occur during a given time period and the number of deaths that actually occurred.

“NCHS has been tracking death data from all causes for decades, so we can estimate the expected number of deaths for any given week with a pretty high degree of confidence.” Lauren says. “We can compare the numbers of deaths we see currently to those expected numbers to see if it’s higher or lower.”

If deaths are higher than average, researchers begin asking more questions: How many of those deaths were caused by COVID-19? What other causes of death, such as Alzheimer’s disease and dementia, are higher than expected? Are those misclassified COVID-19 deaths, or are there other causes of death that are being affected by COVID-19?

Since the pandemic began, Lauren and a team at NCHS have been developing ways to make sure those numbers are available rapidly and are accurate enough to help answer these kinds of questions.

“People are trying to make decisions,” says Lauren. “They need data they can rely on, and they need it quickly.”