> [A]ccording Chris McManus, the researchers made a "very subtle error"...
> Halpern and Coren took a list of the people who had recently died and contacted their families, asking whether or not their relative had been right- or left-handed.
> Looking at 2,000 cases, they saw that the average age at death of the left-handers was about nine years younger than of the right-handers.
> On that basis, they concluded that left-handers died earlier.
> At first glance, that seems persuasive. What did the researchers do wrong?
> "Their mistake was that they only looked at the dead," Chris McManus explains.
> The point is that left-handers are more common now than they used to be, so - at least at the time the research was published - left-handers were on average younger than right-handers.
> Halpern and Coren took a list of the people who had recently died and contacted their families, asking whether or not their relative had been right- or left-handed.
> Looking at 2,000 cases, they saw that the average age at death of the left-handers was about nine years younger than of the right-handers.
> On that basis, they concluded that left-handers died earlier.
> At first glance, that seems persuasive. What did the researchers do wrong?
> "Their mistake was that they only looked at the dead," Chris McManus explains.
> The point is that left-handers are more common now than they used to be, so - at least at the time the research was published - left-handers were on average younger than right-handers.
https://www.bbc.com/news/magazine-23988352