Many may view a measurement of life expectancy as an estimate for how long an average person is expected to live. But in public health, that’s likely not what it actually reflects.
While two primary versions of the metric exist, experts like Dr. Steven Woolf – a professor in the Virginia Commonwealth University School of Medicine whose research frequently deals with the subject – are most often examining what's known as "period" life expectancy. What it reflects from one year to the next can offer clues as to what's weighing down the health of a population or why it may be bouncing back.
“It’s very important in terms of sounding a warning about conditions that are going on within a population,” Woolf says.
Woolf recently spoke with U.S. News about the value of life expectancy as a health metric, public misconceptions about what it reflects and ways in which the measure can inform policies aimed at addressing health inequities.
The interview below has been edited for length and clarity.
What is the value of life expectancy as an indicator of health?
Woolf: It is a statistic that is used to summarize the mortality picture for a population.
To put it in a practical sense, if you were to ask me what the mortality rates are for 2022, as an epidemiologist I would send you a table that tells you the death rates for infants, and the death rates for kids 1 to 4 years old, and the death rates for ages 5 to 9 and so forth all the way through to old age, which would obviously be a very busy table. Instead of doing that I can basically say, “Let’s assume that the whole population experienced the death rates in that table. How long would a newborn live?”
So it’s a shortcut, a composite metric for describing the whole mortality picture for that population.
What is the biggest misconception about life expectancy estimates?
Woolf: It’s widely misunderstood. People think it means that when they’re reporting life expectancy for 2022 that this is how long a baby who is born in 2022 will live, and that’s impossible to know – we don’t have a crystal ball. When people think that’s what it means, it immediately comes under criticism because of all the obvious reasons.
You can’t know where that baby is going to live, for example, and people say that it assumes a person stays in the same place their entire life. It’s not some kind of crystal ball that’s meant to prophesy how long a baby will live; rather, it’s a summary statistic for the mortality of that year.
What can life expectancy tell us about the state of the nation’s health?
Woolf: It’s a commonly used indicator to assess the health of the population, but it’s obviously just one metric. It’s focused very much on death rates, and health is defined by more than death rates. We often – even with regard to mortality rates and survival – talk about not just how long you live, but about the quality of life.
So there are lots of metrics out there, but life expectancy is commonly used. For example, when we do comparisons between the U.S. and other countries, it’s very common to use life expectancy as the barometer for comparing the health of Americans with people in other countries.
COVID-19 had such a large impact on U.S. life expectancy over the past few years. What does life expectancy tell us about longer-term health trends absent events like an infectious disease outbreak?
Woolf: There was a time when the U.S. had higher life expectancy than other high-income countries. Then around the 1980s, the pace at which our life expectancy was increasing started to slow compared to other countries. A gap started developing between the U.S. and our peer countries, and that gap widened progressively over time. By the time we got to 2010, a flatlining occurred and life expectancy stopped increasing altogether, which made the gap widen dramatically.
So that’s a canary in the coal mine for a lot higher rates of disease. Americans are sicker and live shorter lives. Those trends were very much on our minds well before the pandemic arrived. The particular issue in the decade leading up to the pandemic was this rising death toll in young and middle-aged adults, and so a lot of investigation went into the causes of death responsible for that.
How are life expectancy estimates best used in creating health policies?
Woolf: When we saw life expectancy flatlining in the decade prior to the pandemic, that was a very important warning for policymakers that something needed to be done to address the root causes or this massive death toll the U.S. was experiencing was going to widen. The fact that it did not happen in other wealthy democracies indicated that they had been pursuing a set of policies that had protected the health of their populations in ways that we had not done in the U.S. When during the COVID-19 pandemic we sustained much larger losses in life than those other countries, it had to do in large part with policy choices.
That said, it’s not a great metric for tracking progress in policies because life expectancy shifts slowly over time. So we typically look at other kinds of health metrics to measure progress from year to year, and see how we’re doing in improving the health of the population. And over time – like five to 10 years – you start to see measurable changes to life expectancy.
