In epidemiology, there's a metric called "excess death" - they take the average of the last 5-10 years of death records by week or month, and then they have a number of deaths they would expect in that week or month based on historical data. When there's an outbreak causing deaths, you can subtract the normal or "expected" deaths and get a figure called "excess death." It's how much more death we're seeing beyond the typical amount.
This is not necessarily due to the disease. For example, say there's a flood and it caused a cholera outbreak. The flood killed some people and cholera kills others, so epidemiologists will do their best to determine which are due to flood vs. disease. The ones due to the disease based on evidence are called "attributable deaths" - we know what likely caused them. The excess deaths number is a good way to measure, "Ok, if we have 300 flood deaths, and 180 cholera deaths, and 20 unknown, we could account for 500 excess deaths above usual."
For COVID-19, "excess deaths" spiked everywhere experiencing an outbreak, but again, not all caused directly by the disease. Some were people who died at home from something else because they were too worried to go to the hospital, and would have otherwise been preventable. So epidemiologists do the same thing: whoever tested positive for COVID-19, who has pneumonia, who showed symptoms (fever, cough, abnormal clots on autopsy - they're still learning all the signs of this new disease), should equal the excess deaths.
The problem is... they don't equal out like the flood example. There are a lot more excess deaths that have occurred and we don't know why this time. So when scientists say they think it's under reported, it could be because someone died at home and we don't know if they had symptoms beforehand, so they're not categorized. Right now there are a lot of these in areas where a lot of people have been dying of COVID-19 in the hospital. We can't necessarily prove they're COVID-19, and they didn't die of anything else obvious like a car crash, so we just don't know. They're things we suspect are COVID-19 related and later we might learn new things about the disease so we could say, "Oh, he died of a stroke, and we now know COVID-19 can trigger that."
The CDC has a chart with deaths attributable to COVID-19 and the excess deaths we don't know about (you can even filter it by state, and play with some of the other options). You can see there are more unattributable deaths right now, and this is what's led scientists to suspect that COVID-19 is actually being under-counted.
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| Excess Deaths Associated with COVID-19 "Excess deaths with and without COVID-19" dashboard for the United States |
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