Roanoke Times
Copyright (c) 1995, Landmark Communications, Inc.
DATE: MONDAY, March 18, 1991 TAG: 9103160260
SECTION: EXTRA PAGE: E-1 EDITION: METRO
SOURCE: MALCOLM RITTER/ ASSOCIATED PRESS
DATELINE: NEW YORK LENGTH: Long
Now, two scientists say their research suggests southpaws die an average of nine years earlier.
Other researchers are skeptical. "It's provocative, it's hard to believe, and it should be viewed with extreme caution," said Paul Satz of the University of California, Los Angeles, School of Medicine.
But the study's authors say they trust their results, and that they hope identifying the reasons for a longevity difference will help make the world safer for left-handed people.
"By finding these factors maybe we can do something about them," said Stanley Coren of the University of British Columbia in Vancouver, Canada.
Some 10 percent to 13 percent of the population is left-handed. But around 1980 several studies found that left-handedness declines with age. One found it in about 15 percent of people younger than 20, 5 percent of people in their 50s, and virtually nobody 80 or older.
How to explain it? Initially, "the thought that left-handers might be dying off was the farthest things from our minds. It sounded bizarre," Coren recalled.
But he and Diane Halpern of California State University in San Bernardino say two of their studies suggest that may be so. They made their case in the January issue of the Psychological Bulletin.
One study focused on 2,271 dead baseball players. Those who threw and batted with the left hand lived for an average of about 64 years, which was eight months less than the corresponding group of right-handers. Fewer than 0.5 percent of the southpaws lived to age 90, vs. more than 2.5 percent of the right-handers.
The study has been attacked for its statistical analysis. In addition, said psychology Professor Philip Bryden of the University of Waterloo in Ontario, Canada, it was restricted to men who were healthy enough to have played professional baseball. And a player's throwing and batting hand may simply indicate special training rather than his true handedness, Bryden said.
The nine-year longevity gap emerged from a second study. Coren and Halpern sent questionnaires to the next-of-kin listed on 2,875 death certificates filed in two California counties. They got 987 usable responses.
The information let them compare the average life span of the deceased people who wrote, drew and threw with their right hands against that of the others in the sample. They found that the right-handers died at an average age of 75, compared to about 66 for the others. They got about the same answer when they divided the group on the basis only of the writing hand.
"Quite frankly," said Halpern, "I was astounded."
Five left-handedness researchers said they were unconvinced.
"I find this real hard to believe. . . . It's just so outrageous," said psychologist Alan Searleman of St. Lawrence University in Canton, N.Y. Other scientists will have to get the same result before most researchers will accept it, he said.
"If this were really true," he said, "it would have been noticed way before."
Coren disagreed, saying handedness is not listed on death records and "nobody knew to look" for longevity differences before the baseball player study.
Searleman and others suggested the study may have been flawed. Were the reports from the next-of-kin reliable, given that they identified relatively few left-handers among the deceased? Did the next-of-kin who responded really provide a representative sample?
Halpern said next-of-kin probably did erroneously report that some southpaws were right-handed, as prior research says people do. But she said that would tend to obscure a longevity difference, so the fact that one emerged anyway only strengthens her confidence in it.
As to the representativeness of the responding sample, Halpern said that to guarantee anonymity, researchers did not keep track of who responded and who did not. So they could not check to see, for example, if young deaths were especially likely to be reported, she said. Coren said it would be hard to imagine what factors could produce the result by specifically encouraging responses from relatives of short-lived southpaws.
He and Halpern propose a combination of factors to explain why left-handers may die earlier. Their death-certificate study found that southpaws had a higher rate of death from accidental injuries, which fits the notion that southpaws may be put at risk when they operate automobiles and major equipment designed for right-handers.
In addition, many left-handers may be at a medical disadvantage, they say. While some left-handedness is genetic - researchers disagree how much - studies suggest others become left-handed because of very subtle brain injury before or during birth, Coren and Halpern said. Other studies suggest a link between left-handedness and immune system disorders, they said.
Neurological and immunological deficits could reduce the "survival fitness" of left-handers and so shorten lifespan, the researchers proposed.
If all this is true, they say, the accident risk might be reduced through better design of autos and heavy equipment, and perhaps the effects of the medical abnormalities can also be countered.
Although Bryden said he was prepared to accept the eight-month longevity gap suggested by the baseball player study, other researchers familiar with Coren and Halpern's arguments said they were not convinced of any general longevity difference.
Clare Porac of the University of Victoria, British Columbia, said she was willing to entertain the possibility but considered Coren and Halpern's arguments to be backed by inadequate data.
Satz said it is reasonable to suspect that people who are left-handed because of neurological injury could die earlier, but that he doubted genetic left-handers face any such risk. He said he thinks neurological injury probably acounts for only a minority of southpaws.
He and Dr. Albert Galaburda of Beth Israel Hospital in Boston also said it is not clear whether left-handedness is truly linked to immune system disorders.
Some researchers said they think at least part of the age-related decline in left-handedness may come from left-handers switching to using their right hands. Even if switching occurs only in childhood, today's elderly people were children earlier in the century when social pressure against left-handedness was higher, they said.
Coren and Halpern said too few southpaws make the switch to explain the decline.
While research goes on, Coren and Halpern said, left-handers should take their findings in stride. After all, men do not generally panic over the fact that they tend to die younger than women, Coren said.
Halpern said the results are simply statistical associations that do not predict anything about an individual.
Left-handers, she said, should "eat right, exercise, take good care of themselves and not worry about it."
by CNB