LETTERS TO THE EDITOR
education on nursing practice. While identification of published findings, including some in this journal, has been relatively easy, locating unpublished studies has not been. My dissertation, "The Effects of Continuing Education on Nursing Practice: A Meta-Analysis," depends on locating as many studies (both published and unpublished) as possible. If readers of this journal have conducted such a study or impact evaluation and would be willing to share their findings with me, they can send them to me at the address below. Thank you for your assistance. Donna L. Waddell, RN, MSN 811 Drewry Street, NE, Atlanta, GA 30306
Longevity and Left-Handedness While the finding of increased accidents in left-handers is of interest in itself,' the conclusion that accidental death accounts for the low incidence of left-handers in the elderly is not justified. Firstly, a mean difference in life expectancy of 8 months between left and right handers2 is not enough to produce a fall in the incidence of lefthandedness from 13 to 0 percent.3 Secondly, even if all accidental deaths occurred in left-handers, there are not enough accidents to virtually eliminate sinistrals by the age of 80. In the United Kingdom while the incidence of left-handedness falls by 3.8 percent between the ages of 15-70 years,4 only 1.2 percent of deaths between the ages of 15-74 years are attributable to accidents.5 Thirdly, motor vehicle accidents account for about half of accidental deaths (USA 49 percent, UK 40 percent).5 Coren found motor vehicle accidents the only category of accidents significantly commoner in left-handers. If it was the right bias that caused increased mortality in sinistrals, one would expect sinistrals to have a similar life expectancy to dextrals in the UK (where traffic drives on the left) as dextrals would have more traffic accidents. In fact a similar fall in sinistrality with age is found in the UK.4 Although at first it might seem unlikely, some plasticity in handedness into the seventh decade must be part of the explanation of why left-handedness gets less common as populations age. AJPH March 1990, Vol. 80, No. 3
REFERENCES
1. Coren S: Left-handedness and accident-related injury risk. Am J Public Health 1989; 79:10401041. 2. Halpern DF, Coren S: Do right-handers live longer? Nature 1988; 333:213. 3. Porac C, Coren S, Duncan P: Life-span age trends in laterality. J Gerontol 1980; 35:715-721. 4. Ellis SJ, Ellis PJ, Marshall E: Hand preference in a normal population. Cortex 1988; 24:157163. 5. World Health Organization: World Health Statistics Annual 1988. Geneva: WHO, 1988. Simon J. Ellis, MRCP Mount Sinai Medical Center, One Gustave L. Levy Place, New York, NY 10029-6574.
deaths for sinistrals and dextrals, however, we are acting conservatively, since it is known that other, non-accident-related factors increase the risk of early death in left-handers (e.g., reduced immune system function or birth stress related pathologyl'2). The above computations illustrate that the cumulative effect of a small elevation in risk may well result in the reduction of the population proportion of left-handers in older age groups without recourse to arguments about the plasticity of handedness.
© 1990 American Journal of Public Health
Response from Professor Coren To explain the reduction in the proportion of left-handers in the population, from 13 percent in 20 year olds to less than 1 percent in 80 year olds,' we suggested that left-handers may have shorter life spans2 and may be more subject to accident-related death than right-handers.3 This suggestion is not based upon the mean difference in life expectancy of 8 months, but rather upon the observation that, beyond age 33, the annual risk of death in sinistrals is 1 to 2 percent higher.2 The effect of this elevated risk is cumulative, eventually resulting in a marked reduction in the relative number of left-handers. This can easily be demonstrated using simple mathematical modeling and some arbitrary values to illustrate the point. Suppose that the annual likelihood that a right-handed individual will die is split evenly between accident and nonaccident related causes, each at 0.03. For left-handers, the probability for non-accident related death remains the same at 0.03, while the relative risk of accident-related injury (and therefore accident-related death) is 1.89 higher,3 hence 0.057. With a sample of 10,000 individuals aged 20, we would have 1300 sinistrals and 8700 dextrals for 13 percent left-handedness.' By the time the survivors reach 80 years of age (60 iterations of the model) the population has been reduced to 212 dextrals and 5 sinistrals, for a population percentage of left-handers of only 2.5 percent. While the rate of death by accident selected here was arbitrary, and probably a bit high, there is evidence that accidents, when they are the underlying cause of death, may be underreported by as much as 86 percent.4 By equating the probability of non-accident-related
REFERENCES 1. Halpern DF, Coren S: Do right-handers live longer? Nature 1988; 333:213. 2. Coren S: Left-handedness and accident-related injury risk. Am J Public Health 1989; 79:10401041. 3. Porac C, Coren S, Duncan P: Life-span age trends in laterality. J Gerontol 1980; 35:715-721. 4. Waller JA: Falls among the elderly: Human and environmental factors. Accid Anal Prev 1978; 10:21-33.
Stanley Coren Ph D Professor of Psychology, University of British Columbia, 2136 West Mall, Vancouver, B.C. Canada V6T 1Y7 C 1990 American Journal of Public Health
Lead Exposure in Indoor Firing Ranges The paper entitled "Lead Absorption in Indoor Firing Range Users" by Valway, et al in the August 1989 issue provides a valuable indication of the contribution of indoor shooting range activity to lead exposure. However, in evaluating the acceptability of their study environment relative to airborne levels of lead measured during shooting activity, the authors appear to incorrectly apply the 8-hour time-weighted exposure concept inherent in the OSHA Permissible Exposure Limit (PEL). The authors correctly state that the OSHA PEL for lead is 50 ,ug/m3 as an 8-hour time-weighted average. This means that the concentration in air at any time may exceed the PEL value as long as the average concentration over the course of an 8-hour work day does not exceed this level. The authors also state that "the overall mean air lead concentration for all booths . . . was >2000 ,ug/m3." The authors then conclude that "At this concentration, the OSHA permissible exposure level ... was exceeded within 12 minutes of shooting." 353
education on nursing practice. While identification of published findings, including some in this journal, has been relatively easy, locating unpublished studies has not been. My dissertation, "The Effects of Continuing Education on Nursing Practice: A Meta-Analysis," depends on locating as many studies (both published and unpublished) as possible. If readers of this journal have conducted such a study or impact evaluation and would be willing to share their findings with me, they can send them to me at the address below. Thank you for your assistance. Donna L. Waddell, RN, MSN 811 Drewry Street, NE, Atlanta, GA 30306
Longevity and Left-Handedness While the finding of increased accidents in left-handers is of interest in itself,' the conclusion that accidental death accounts for the low incidence of left-handers in the elderly is not justified. Firstly, a mean difference in life expectancy of 8 months between left and right handers2 is not enough to produce a fall in the incidence of lefthandedness from 13 to 0 percent.3 Secondly, even if all accidental deaths occurred in left-handers, there are not enough accidents to virtually eliminate sinistrals by the age of 80. In the United Kingdom while the incidence of left-handedness falls by 3.8 percent between the ages of 15-70 years,4 only 1.2 percent of deaths between the ages of 15-74 years are attributable to accidents.5 Thirdly, motor vehicle accidents account for about half of accidental deaths (USA 49 percent, UK 40 percent).5 Coren found motor vehicle accidents the only category of accidents significantly commoner in left-handers. If it was the right bias that caused increased mortality in sinistrals, one would expect sinistrals to have a similar life expectancy to dextrals in the UK (where traffic drives on the left) as dextrals would have more traffic accidents. In fact a similar fall in sinistrality with age is found in the UK.4 Although at first it might seem unlikely, some plasticity in handedness into the seventh decade must be part of the explanation of why left-handedness gets less common as populations age. AJPH March 1990, Vol. 80, No. 3
REFERENCES
1. Coren S: Left-handedness and accident-related injury risk. Am J Public Health 1989; 79:10401041. 2. Halpern DF, Coren S: Do right-handers live longer? Nature 1988; 333:213. 3. Porac C, Coren S, Duncan P: Life-span age trends in laterality. J Gerontol 1980; 35:715-721. 4. Ellis SJ, Ellis PJ, Marshall E: Hand preference in a normal population. Cortex 1988; 24:157163. 5. World Health Organization: World Health Statistics Annual 1988. Geneva: WHO, 1988. Simon J. Ellis, MRCP Mount Sinai Medical Center, One Gustave L. Levy Place, New York, NY 10029-6574.
deaths for sinistrals and dextrals, however, we are acting conservatively, since it is known that other, non-accident-related factors increase the risk of early death in left-handers (e.g., reduced immune system function or birth stress related pathologyl'2). The above computations illustrate that the cumulative effect of a small elevation in risk may well result in the reduction of the population proportion of left-handers in older age groups without recourse to arguments about the plasticity of handedness.
© 1990 American Journal of Public Health
Response from Professor Coren To explain the reduction in the proportion of left-handers in the population, from 13 percent in 20 year olds to less than 1 percent in 80 year olds,' we suggested that left-handers may have shorter life spans2 and may be more subject to accident-related death than right-handers.3 This suggestion is not based upon the mean difference in life expectancy of 8 months, but rather upon the observation that, beyond age 33, the annual risk of death in sinistrals is 1 to 2 percent higher.2 The effect of this elevated risk is cumulative, eventually resulting in a marked reduction in the relative number of left-handers. This can easily be demonstrated using simple mathematical modeling and some arbitrary values to illustrate the point. Suppose that the annual likelihood that a right-handed individual will die is split evenly between accident and nonaccident related causes, each at 0.03. For left-handers, the probability for non-accident related death remains the same at 0.03, while the relative risk of accident-related injury (and therefore accident-related death) is 1.89 higher,3 hence 0.057. With a sample of 10,000 individuals aged 20, we would have 1300 sinistrals and 8700 dextrals for 13 percent left-handedness.' By the time the survivors reach 80 years of age (60 iterations of the model) the population has been reduced to 212 dextrals and 5 sinistrals, for a population percentage of left-handers of only 2.5 percent. While the rate of death by accident selected here was arbitrary, and probably a bit high, there is evidence that accidents, when they are the underlying cause of death, may be underreported by as much as 86 percent.4 By equating the probability of non-accident-related
REFERENCES 1. Halpern DF, Coren S: Do right-handers live longer? Nature 1988; 333:213. 2. Coren S: Left-handedness and accident-related injury risk. Am J Public Health 1989; 79:10401041. 3. Porac C, Coren S, Duncan P: Life-span age trends in laterality. J Gerontol 1980; 35:715-721. 4. Waller JA: Falls among the elderly: Human and environmental factors. Accid Anal Prev 1978; 10:21-33.
Stanley Coren Ph D Professor of Psychology, University of British Columbia, 2136 West Mall, Vancouver, B.C. Canada V6T 1Y7 C 1990 American Journal of Public Health
Lead Exposure in Indoor Firing Ranges The paper entitled "Lead Absorption in Indoor Firing Range Users" by Valway, et al in the August 1989 issue provides a valuable indication of the contribution of indoor shooting range activity to lead exposure. However, in evaluating the acceptability of their study environment relative to airborne levels of lead measured during shooting activity, the authors appear to incorrectly apply the 8-hour time-weighted exposure concept inherent in the OSHA Permissible Exposure Limit (PEL). The authors correctly state that the OSHA PEL for lead is 50 ,ug/m3 as an 8-hour time-weighted average. This means that the concentration in air at any time may exceed the PEL value as long as the average concentration over the course of an 8-hour work day does not exceed this level. The authors also state that "the overall mean air lead concentration for all booths . . . was >2000 ,ug/m3." The authors then conclude that "At this concentration, the OSHA permissible exposure level ... was exceeded within 12 minutes of shooting." 353
