"[The researchers] 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?"
Can you guess what they did wrong? For the answer, read the article in the BBC.