900,000 more people died in 2021 than expected.

“Excess Deaths”. You’ve heard the phrase countless times by now. It is one of the myriad of previously esoteric epidemiology terms that the pandemic brought squarely into the zeitgeist.

As a sort of standard candle of the performance of a state, or a region, or a country in terms of healthcare it has a lot of utility – if for nothing more than Monday morning quarterbacking.  But this week, I want to dig in on the concept a bit because, according to a new study, the excess death gap between the US and Western Europe has never been higher.

Ok what do we mean when we say “excess mortality”?  The central connotation of the idea is that there are simply some deaths that should not have occurred. You might imagine the best way to figure this out is for some group of intelligent people to review each death and decide, somehow, whether it was expected or not. But aside from being impractical this would end up being somewhat subjective. That older person who died from pneumonia – was that an expected death? Could it have been avoided?

So rather the calculation of excess mortality relies on large numbers and statistical inference to compare an expected number of deaths to those that are observed.

The difference is excess mortality, even if you can never be sure whether any particular death was expected or not.

As always, the devils is in the details though. What data do you use to define the expected number of deaths?

There are options here. Probably the most straightforward analysis uses past data from the country of interest. You look at annual deaths over some historical period of time, and compare those numbers to the rates today. Two issues need to be accounted for here. One – population growth – a larger population will have more deaths, so you need to adjust the historical population to current levels. Two – demographic shifts – an older or more male population will have more deaths, so you need to adjust for that as well.

But provided you take care of those factors, you can estimate fairly well how many deaths you can expect to see in any given period of time.

Still – you should see right away that excess mortality is a relative concept. If you think that, just perhaps, the US has some systematic failure to deliver care that has been stable and persistent over time, you wouldn’t capture that failing in an excess mortality calculation that uses US historical data as the baseline.

The best way to get around that is to use data from other countries, and that’s just what this article – a rare single author piece by Patrick Heuveline does – calculating excess deaths in the US by standardizing our mortality rates to the five largest Western European countries: The UK, France, Germany, Italy, and Spain.

Controlling for the differences in the demographics of that European population, here is the expected number of deaths in the US over the past five years.

Note that there is a small uptick in expected deaths in 2020, reflecting the pandemic, which returns to baseline levels by 2021. This is because that’s what happened in Europe – by 2021 the excess mortality due to COVID-19 was quite low.

Here are the actual deaths in the US during that time.

Highlighted here in green is the excess mortality over time in the United States.

There are some fascinating and concerning findings here.

First of all, you can see that, even before the pandemic, the US has an excess mortality problem. This is not entirely a surprise – we’ve known that so-called “deaths of despair”, those due to alcohol abuse, drug overdoses, and suicide are at an all-time high and tend to affect a “prime of life” population that would not otherwise be expected to die. In fact, fully 50% of the excess deaths in the US occur in those between ages 15 and 64.

Excess deaths are also a concerning percentage of total deaths. In 2017, 17% of total deaths in the US could be considered “excess”. In 2021, that number had doubled to 35%. Nearly 900,000 individuals in the US died in 2021 that, perhaps, didn’t need to.

The obvious culprit to blame here is COVID, but COVID-associated excess deaths only explain about 50% of the excess we see in 2021. The rest reflect something even more concerning – a worsening of the failures of the past, perhaps exacerbated by the pandemic, but not due to the virus itself.

Of course, we started this discussion acknowledging that the calculation of excess mortality is exquisitely dependent on how you model the expected number of deaths, and I’m sure some will take issue with the use of European numbers when applied to Americans. After all, Europe has, by and large, a robust public health service, socialized medicine, and healthcare that does not run the risk of bankrupting its citizens. How can we compare our outcomes to a place like that?

How indeed.

A version of this commentary first appeared on Medscape.com