“When you see life expectancy reported, about 95% of the time, it’s the period life expectancy measure,” said Michel Guillot, a demographer and professor of sociology at the University of Pennsylvania. “It is based on the concept of a synthetic or fictitious cohort.” The statistic looks at how many people died at each age in a given year, and then calculates how long a hypothetical infant would live if those age-specific death rates applied for that infant’s entire life. For example, if 1.5% of people aged 65 died in 2022, this calculation assumes 1.5% of babies born this year who are still alive in 65 years will die at that age. But, of course, today’s babies won’t actually turn 65 until the late 2080s, and that would be an extraordinarily long time for us to make no progress on mortality. The more relevant way to measure how long a child born today will actually live is with “cohort life expectancy.” In the past 20 years, death rates from cancer, heart disease, and stroke have all fallen dramatically. There is reason to think that should continue.
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