The ONS (‘Office of National Statistics) produces annual updates on period life expectancy in the UK – the so-called National Life Tables. The latest tables are based on the 2018 to 2020 period, and therefore are the first to pick up the impact of the COVID-19 pandemic. Given the significantly increased death rates seen in 2020, this fall in life expectancy is not unexpected. However, it is important to note that the headline figures hide a wide variety of underlying impacts at a more granular level.
Now, because the pandemic produced higher death rates in 2020 compared to prior years, a period life expectancy calculated for 2020 produced lower life expectancies compared to period life expectancies calculated for prior years. That’s because it’s assumed that the elevated death rates we experienced in 2020 would apply to all future years. But if the death rates decline in 2021, then any period life expectancies calculated for 2021 would most likely be higher. And that’s certainly the hope, given that a large portion of the population has received a vaccine, which is already resulting in a dramatic decline in new infections and hospitalizations.
If you’ve survived the pandemic with your health relatively intact and if you’ve also received the vaccine, then it’s highly likely the virus won’t shorten your lifespan. Of course, new deadly variants or future deadly viruses could change that conclusion, but for now, the outlook is positive.
“Cohort life expectancies” on the other hand, are calculated for a group of people reflecting their characteristics and the experience they might expect over their lifetimes. These life expectancies are calculated in the same way as period life expectancies, except that the death rates used to estimate someone’s remaining future years are modified to reflect anticipated future changes in death rates. If you want to estimate your own remaining lifespan, a cohort life expectancy is often most appropriate.
It is better to provide death rates by age ranges for year-to-year comparisons.
When you calculate a period life expectancy, you’re incorporating the mortality rates for all the ages above the current age, and it doesn’t really capture how specific age ranges were affected. I can use these life expectancies to make estimates about the death rates, but I’m not going to – I’m trying to keep the calculations simple so that other people can follow my spreadsheets and check what I’m doing.
With age-adjusted death rates, you can capture overall mortality levels, but again, you don’t know which age ranges were affected the most.
I believe period life expectancy is used for these types of reports because people are more comfortable thinking about number of years to live, or age at death, than they are thinking about rates.