Death clocks should come with a health warning, says top economist

The good news is that we are all living longer. The bad news is that we will all die ... but when?

In The BMJ today, John Appleby, Chief Economist at the Nuffield Trust, uses online "death clocks" to calculate the date of his demise, but finds that his life expectancy varies depending on who he asks.

Knowing when you are going to die could help make life choices, he writes, but he suggests that death clocks should come with a health warning—and the results should be taken with a pinch of salt.

Data from the Office for National Statistics (ONS) period life tables estimate life expectancy at birth averaged across the three years of 2013 to 2015 to be around 79 years for boys and 83 for girls, explains Appleby.

And over the past 33 years, average life expectancy at birth for UK residents has been increasing by, on average, 13.1 weeks per year for boys and 9.5 weeks for girls.

Of course, many factors can affect life expectancy, such as genetics, lifestyle, wealth, education and employment. Being married, for example, can add over a year to life expectancy compared with being single. And one study even suggests that optimists have a 55% lower risk of early death than pessimists.

But for a more individual perspective, he says you need to adjust these figures for personal characteristics and circumstances.

Based on his sex and the current mortality for his age group, ONS life tables suggest Appleby will die around May 2040, about a month after his 82nd birthday.

But plugging in a few more personal details - such as his marital status, income, and stress levels - into a random selection of online death clocks produced a range of predictions for his life expectancy from 67 to 89!

Some of the variation in predictions is due to differences in the basic life table data that the clocks use (some are based on non-UK data for example), he explains.

Differences will also arise given the particular risk calculators (prediction models) used, the number of variables included, and the way they combine variables to produce individualised forecasts.

So perhaps the only safe conclusion is that death clocks should come with a health warning, he concludes. "Calculating the date of your demise is somewhat sobering and the results should be taken with a pinch of salt."