Release Date: February 17, 1994
BUFFALO, N.Y. -- There is little difference in the longevity of left- and right-handers up until age 65, and right-handers live only about one year longer than left-handers from age 65 on, a University at Buffalo geographer has found.
The findings of Peter Rogerson, professor and chair of geography at UB, differ strikingly from those of earlier studies that estimated that right-handers live up to nine years longer than left-handers.
In a study to be published in a forthcoming issue of Social Biology, Rogerson looked at the handedness, vital status, age at beginning of career, date of birth and date of death for 4,448 baseball players listed in "The Sports Encyclopedia: Baseball." Only those players born before 1920 were included in the study. The study also was limited to players listed as using the same hand for batting and throwing.
Using two statistical tests to compare the survival curves of left- and right-handers, Rogerson determined that the survival rates were similar for both groups between the ages of 25 and 65. However, the survival rates of right-handers between the ages of 65 and 85 were noticeably higher than those for left-handers in that age group. He found that 21 percent of left-handers alive at age 65 would be alive at age 85, while 26 percent of right-handers alive at 65 would be alive at 85.
He calls the difference in longevity "noticeable but small," saying that right-handed 65-year-olds "can expect to live close to one year longer, plus or minus a little more than half a year."
"There's something to it," Rogerson says of the theory that right-handers live longer than left-handers. But the difference in longevity for the two groups "is not as startling" as some studies have suggested.
He says that while these other studies have looked only at persons who had died, his sample included persons who were still living.
"It's important to look at those who are still alive because they give us more information," he says. "Those who have died are just part of the sample.
"For example, a conclusion, based upon data on deceased individuals, that right-handers live longer may in fact be negated if relatively more of the left-handers remain alive.
"Even with no differences in longevity, it might still be expected from an analysis of the deaths in a given period that left-handers would have a lower mean age at death, since some evidence indicates that the incidence of left-handedness has increased over time."
The incidence of left-handedness has increased, Rogerson says, because many natural left-handers no longer are forced, as children, to use their right hands.
Rogerson says his study also differs from others in that he used a much larger sample than most previous studies. The sample size is large enough, he adds, that the results cannot be attributed to chance.
He notes that if there are small differences in the longevity of right-handers and left-handers between the ages of 25 and 65, they are harder to detect in samples of this size because of the small number of deaths in this age range.
He says the difference in longevity among those over 65 might be due to the relationship between handedness and stress at birth. Arguments have been made by some researchers that left-handers experience more prenatal and perinatal stress, which links them to a variety of disorders, including smoking and alcoholism, breast cancer, early-onset Alzheimer's disease and schizophrenia.
Rogerson believes the best argument linking left-handers with decreased longevity is a concept called the Rare Trait Marker Model.
According to the model, there is some "pathological intervention" that interrupts the natural distribution of handedness and causes a percentage of the population to switch its handedness to the side opposite the naturally determined side of preference.
For example, in a population that is 90 percent right-handed and 10 percent left-handed, some individuals -- say 10 percent -- would suffer some stress that would switch their handedness. According to the model, 9 percent of the natural right-handers would become left-handers and 1 percent of the natural left-handers would become right-handers, leaving a population that is 82 percent right-handed and 18 percent left-handed.
In this left-handed population, half would have this preference because of the intervening pathology. The probability of finding a "pathological individual" -- one who would have a decreased survival rate -- in the left-handed group would be 42 times greater than the probability of finding one in the right-handed group.
The UB study was supported by a grant from the National Science Foundation and by a National Science Presidential Young Investigator Award.