Lefties and longevity: look again.
A fresh analysis of data from an encyclopedia of baseball statistics should pitch some relief to left-handed people. Contrary to earlier conclusions drawn from similar data, the new calculations suggest lefties do not die younger than their right-handed counterparts. Indeed, in the newest measure of the relationship between handedness and longevity, southpaws appear to enjoy a mild survival advantage. But that finding, too, stirs controversy.
For the past decade, researchers have debated the significance of handedness in mortality rates. The percentage of U.S. left-handers decreases with increasing age, dropping to virtually zero among 80-year-olds. Since few lefties appear to change handedness after childhood, some researchers have surmised that the decrease might stem from lower survival rates among left-handers. Possible explanations for such increased mortality include higher accident rates (either naturally or because tools, machinery and even traffic patterns are designed for the convenience of right-handed people) or some genetic linkage with life-shortening prenatal or immune disorders.
To settle the issue, two researchers last year undertook a retrospective analysis of 2,271 deceased professional baseball players. Psychologists Diane F. Halpern of California State University at San Bernardino and Stanley Coren of the University of British Columbia in Vancouver (both right-handed) tallied relative survival rates for all baseball players in The Baseball Encyclopedia (Macmillan, 1979). After throwing out any players showing evidence of ambidexterity, they found that for players who lived beyond age 33, the annual survival rate of right-handers exceeded that of lefties by about 2 percent.
But Max G. Anderson, a left-handed number cruncher with the Canadian Statistical Analysis Service in Vancouver, suspected those statistics masked the truth. Using essentially the same data (a more recent edition of a sports encyclopedia), he sorted baseball players by year of birth and came to a different conclusion: Right-handers used to live longer -- but not anymore, he reports in the Sept. 14 NATURE. He finds left-handed baseball players born after 1890 have in general outlived their non-lefty contemporaries. Moreover, the survival gap -- already surpassing 2 years, he calculates -- appears to be widening.
Previous analyses "overlooked what I consider to be a better way of analyzing the data," Anderson says. Since U.S. life-spans have increased significantly in the past 100 years, "you wouldn't want to lump [players] all together over a century." Anderson hypothesizes that left-handedness evolved along with other, unrecognized genetic traits that have helped compensate for the cultural and physical biases inherent in a world historically dominated by a right-handed majority. With discrimination against left-handers now less prevalent, he contends, lefties may prove hardier than righties.
Coren disagrees. He says Anderson's analysis does not exclude ambidextrous players as thoroughly as does his and Halpern's. And he claims there is little evidence that left-handed life today is any less dangerous than in previous times. The researchers' disparate conclusions may also stem from Anderson's inclusion of players who died younger than 33. Halpern and Coren -- for reasons they cannot explain -- found no associations between mortality and handedness in this group.
Last month, Coren published data showing a link between left-handedness and higher accident rates among college students, with especially high relative risks for left-handed males driving motor vehicles. He and Halpern have begun analyzing data from a new study of California death records that he says will provide a needed expansion beyond baseball statistics, which may not apply to the general population.
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|Date:||Sep 16, 1989|
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