Studies on Left-Handedness
Two recent articles (April 4 and Feb. 13) have featured studies that are critical of the research that I have conducted with Stan Coren at the University of British Columbia in which we concluded that left-handedness is associated with reduced longevity. These reports have largely ignored the huge research literature that supports our conclusion. The major criticism of our work is that the decline in left-handers had been “switched” to right- hand use. There are many reasons why we believe that “switching” cannot account for these results.
First, when natural left-handers were forced to switch their preferred hand, eating and writing were, almost always, the only targeted activities. Most “switched” lefties who learned to eat or write with their right hand still continued to perform other activities with their left hand (or foot, a related variable that was not subject to social pressures) such as throwing or kicking a ball, drawing, and striking a match. For this reason, researchers ask respondents about tasks other than writing and eating so that we are not labeling switched left-handers as right-handers. Numerous studies also show that attempts to switch a strong left-hander (people vary in the extent to which they are left- or right-handed) to right hand use are usually unsuccessful.
Those studies that attempt to explain the decline in left-handers as a function of age with the “switching hypothesis” also fail because the percentage of individuals who state that they were subject to pressures to change from left to right-hand use is not large enough to explain the decline in left-handers as a function of age. The age-related decline in left-handedness was documented in the research literature over 80 years ago, long before the purported liberalization of attitudes toward left-hand use. Finally, six handedness surveys published in the period 1928 through 1933 (when today’s oldest citizens were young) show the same proportion of left-handedness in the population that researchers find in current surveys. There are several studies that show an increased risk of accidents for left-handers including studies that found a larger proportion of serious accidents (such as emergency room visits, surgery for injuries, and head injuries serious enough to cause loss of consciousness). The accident data is particularly important because accidents cause a very large average loss of life years.
Most importantly, no article on this topic should appear without the explicit statement that there is no cause for alarm. These are statistical associations based on large group data and no one is “average.” There are many advantages to left-handedness, in addition to the ones that are well known in sports. As a group, left-handers are overrepresented among mathematically gifted youth and in many scientific and creative fields. There are many very old left-handers.
DIANE F. HALPERN
Professor of Psychology
Cal State San Bernardino
