CDC estimated a one-year decline in life expectancy in 2020. Not so — try five days

The Centers for Disease Control and Prevention made headlines last week when it announced that Covid-19 had reduced the average life expectancy of Americans in 2020 by a full year. The news seemed to starkly illustrate the devastation wrought by our nation’s worst public health crisis in 100 years.

But there was a problem. The pandemic’s appalling toll could not have reduced life span by nearly that much. My own estimate is that when Covid-19’s ravages in 2020 are averaged across the country’s entire population, we each lost about five days of life.

The CDC’s mistake? It calculated life expectancy using an assumption that is assuredly wrong, which yielded a statistic that was certain to be misunderstood. That’s exactly the type of misstep the agency can’t afford to make. Not now, not after former President Trump’s relentless attacks on its credibility. Not after his advisers were caught altering and editing the agency’s monthly reports to downplay the pandemic.

To review: The CDC reported that life expectancy in the U.S. declined by one year in 2020. People understood this to mean that Covid-19 had shaved off a year from how long each of us will live on average. That is, after all, how people tend to think of life expectancy. The New York Times characterized the report as “the first full picture of the pandemic’s effect on American expected life spans.”

But wait. Analysts estimate that, on average, a death from Covid-19 robs its victim of around 12 years of life. Approximately 400,000 Americans died Covid-19 in 2020, meaning about 4.8 million years of life collectively vanished. Spread that ghastly number across the U.S. population of 330 million and it comes out to 0.014 years of life lost per person. That’s 5.3 days. There were other excess deaths in 2020, so maybe the answer is seven days lost per person.

No matter how you look at it, the result is a far cry from what the CDC announced.

It’s not that the agency made a math mistake. I checked the calculations myself, and even went over them with one of the CDC analysts. The error was more problematic in my view: The CDC relied on an assumption it had to know was wrong.

The CDC’s life expectancy calculations are, in fact, life expectancy projections (the technical term for the measure is period life expectancy). The calculation is based on a crucial assumption: that for the year you are studying (2019 compared to 2020 in this case) the risk of death, in every age group, will stay as it was in that year for everyone born during it.

So to project the life expectancy of people born in 2020, the CDC assumed that newborns will face the risk of dying that newborns did in 2020. Then when they turn 1, they face the risk of dying that 1-year-olds did in 2020. Then on to them being 2 years old, and so on.

Locking people into 2020 for their entire life spans, from birth to death, may sound like the plot of a dystopian reboot of “Groundhog Day.” But that’s the calculation. The results: The CDC’s report boils down to a finding that bears no relation to any realistic scenario. Running the 2020 gauntlet for an entire life results in living one year less on average than running that same gauntlet in 2019.

Don’t blame the method. It’s a standard one that over time has been a highly useful way of understanding how our efforts in public health have succeeded or fallen short. Because it is a projection, it can (and should) serve as an early warning of how people in our society will do in the future if we do nothing different from today.

But in this case, the CDC should assume, as do we all, that Covid-19 will cause an increase in mortality for only a brief period relative to the span of a normal lifetime. If you assume the Covid-19 risk of 2020 carries forward unabated, you will overstate the life expectancy declines it causes. It’s not like I am the first person to notice this problem. Researchers have regularly demonstrated that life expectancy projections are overly sensitive to evanescent events like pandemics and wars, resulting in considerably overestimated declines.

And yet the CDC published a result that, if anything, would convey to the public an exaggerated toll that Covid-19 took on longevity in 2020. That’s a problem.

Please don’t misunderstand: I have no desire to play down this horrific pandemic. The U.S. recently surpassed a half-million deaths, the highest number of deaths of any country. Instead, I mean to emphasize that the CDC must remain the world’s gold standard public health agency, and that means working tirelessly to get both its facts and its messages right.

The agency won’t always succeed. But after four years of an administration that claimed infallibility, even as the pile of errors reached staggering heights, we should hold this administration’s CDC to the highest possible standard.

I have been wondering if the CDC should withdraw this report, explaining that it erred by disseminating a finding that was bound to be misunderstood. Yes, Covid-19 deniers will try to score cheap political points for a day or two. But at least for me, I don’t need an agency that is flawless, but one that is forthright.

Peter B. Bach is a physician at Memorial Sloan Kettering Cancer Center, where he directs the Center for Health Policy and Outcomes.