Demystifying science | Left-handers more at risk?

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Is it true that left-handers live shorter lives than right-handers?
—Benoit Carbonneau

The results of a 1991 study, which claimed that left-handers live shorter lives than right-handers, have been repeatedly refuted.

In 1991, these researchers analyzed the deaths of left-handed and right-handed people. However, left-handers were numerous among the younger generation, but practically absent among the older generations. For what ? Until the 1960s or even 1970s, left-handers were taught to write with their right hand, explains Olga Basso, an epidemiologist at McGill University who published a study on the subject in 2000. This introduced distortion and gave the The impression that left-handers died younger, because there were fewer old left-handers.

The 1991 study, conducted among 1,000 Californians in 1989 by researchers at the Universities of Southern California and British Columbia, concluded that left-handers died nine years younger than right-handers. Published in the prestigious journal New England Journal of Medicine, she claimed that the technology was made for right-handers and therefore riskier for left-handers. The same authors published in 1988 in Nature a study of 2,271 baseball players concluded that each year, left-handers were between 1% and 2% more likely to die.

Danish twins

The recent rebuttal of the 1991 study was made by Harvard University epidemiologist Subu V. Subramanian, along with Microsoft researchers who simulated the mortality rates left-handers of yesteryear would have had if they did not They weren’t forced to be right-handed. “The 1991 study was purely observational, but said there was causality,” says Subramanian, who published his study last summer in the journal Archives of Public Health. “We show that even the observational association was not robust,” because the authors of the 1991 study did not take into account ostracism against left-handers.

Olga Basso, a McGill University epidemiologist who published her 2000 study in the journal Epidemiology while working at the University of Aarhus in Denmark, analyzed 118 pairs of Danish twins born between 1900 and 1910. Each pair of twins included one right-handed and one left-handed and no impact of this variable on mortality had been observed.

It is possible that in certain subpopulations there is a greater risk of mortality among left-handed people, according to Mr. Subramanian. “We didn’t check what was happening in different ethnic groups and gender. There is no data on the subject. But on average, there is no effect of being left or right-handed on mortality risk. »

One of the most prolific researchers in the field, Chris McManus of University College London, is now retired. In 2010, in the magazine Laterality, it showed that the war on left-handers, at least in the West, had been a phenomenon extending over three centuries. Before the 18th century^e century, the rate of left-handed people was around 10%, like today. At the beginning of the 20th^e century, they had experienced a rate of only 2%.

The largest study on the subject, published in 1994 in Behavior Genetics by American researchers, used data from 32 countries to arrive at a proportion of left-handed people of 9.5%.

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