Sep. 28, 2000 Erie, Pa -- Although the percentage of left-handed people among those over age 60 is lower than in the rest of the population, there is no indication that left-handedness leads to an early demise. Rather, a complex combination of factors combine so that fewer of the old and oldest old report left-handedness, according to a Penn State researcher.
Some factors involved include pressure to switch hands, more women than men in the older populations, adaptation to a predominantly right-hand world and a rightward trend caused by the aging process.
"Recent work reports that over 80 percent of left-handers older than 75 remember an attempt to switch hand preference to the right side as compared with a report rate of 24 percent among young adult left-handers," says Dr. Clare Porac, professor of psychology and director, School of Humanities and Social Sciences, Penn State Erie, the Behrend College.
When those over 75 years were children, pressures to change preference from left-handed to right-handed, especially for writing, were strong. Since then, these pressures have lessened greatly.
Porac and Ingrid C. Friesen, Ph.D. candidate, University of Victoria, looked at studies of age difference in the incidence of right and left-hand preference published since 1980. They found two possible sources of confusion related to the exact nature of age-related differences in hand preference.
"Relatively few individuals over the age of 60 participated in hand preference research over this 20-year period," says Porac. Also, the various studies used differing methods to define the oldest group and some included children in their studies while others did not.
In their own study, reported in a recent issue of Developmental Neuropsychology, the researchers looked at 1,277 elderly people to determine the incidence of left versus right handedness, if this incidence was age related and the relationship of handedness to life experiences such as efforts to switch left handers to a right-hand preference. The study included both older adults -- aged 60 to 74 -- and oldest-old adults -- aged 75 or over.
Participants were asked which hand they used for five actions -- writing, picking up an object, throwing, striking a match and eating with a fork without a knife. These particular activities were chosen to encompass both skilled and unskilled actions -- writing and picking up an object -- and culturally pressured and unpressured behaviors -- writing and throwing.
Overall, they classified 6.9 percent of the individuals as left-handed and 93.1 percent as right handed. At the same time, 10.3 percent reported an attempt to convert a left-handed preference to right handedness, while only 1.8 reported an attempt to shift toward left handedness. The remaining 87.9 percent indicated no attempt to change hand preference.
The researchers then divided the participants into four age groups -- 65 to 69, 70 to 73, 75 to 79, and 80 to 100 -- and looked at individual activities.
"Age-related reduction in the incidence of left-hand preference across the 35-year age span of the participants in this study was found only for the writing hand behavior," says Porac.
As the age of the subgroups increased, so did the incidence of right-handed writing. For the youngest group (65 to 69), 6.8 percent were left-handed writers, while for the oldest group (80 to 100) only 3 percent were left-handed writers. For the oldest-old group, the number of left-handed writers was 5 to 6 percent lower than the number of people who indicated a preference for left-handedness in the other three categories.
Pressures in the first quarter of the past century to force children to write right handed appear to have had some effect, but they do not totally account for all the discrepancy in the amount of left-handed people in elderly and young populations. Gender differences in the make-up of the oldest old population may have an effect because women predominate in populations of the oldest old.
"The data revealed that women over the age of 73, who had experienced a rightward shift attempt, showed a very low incidence of left-hand writing compared to men," says Porac. "Women are more likely to report being pressured to switch their hand preference and are more frequently among those who have been shifted to the right side successfully."
Even accounting for high numbers of women, the numbers of left-handed oldest old are still too low. Porac suggests that with increasing age, biologically related developmental effects shift toward right-sided preference. This is exhibited in a shift toward right footedness as well.
One other factor may be that left-handed people shift their hand preference to accommodate pressures of a right-handed world. While more research is needed to account for the existing discrepancy, the researchers believe that the shift to right-handedness is not caused by a propensity for accidents or premature death.
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