LETTERS TO THE EDITOR
would assume that there are no lives being saved because of ROPS. Yet I know much better since I have information on at least 35 overturn incidents in Nebraska where ROPS were in place and lives saved. This was done as part of the voluntary program in Nebraska and not because of a government requirement. Without ROPS, 40 per cent of the operators of the tractor overturns should have been killed. This figure is taken from a Nebraska overturn study that was started in 1966, 10 years before the OSHA standard came into being. That study has been continued since 1966. I know how the accidents happened since staff of the Department of Agricultural Engineering were involved in researching the site of the tractor overturns. I am familiar with the history of roll over protective structures. The Department of Agricultural Engineering at the University of Nebraska played an important part in the development of ROPS. Also, I served as chairman of the Agricultural Advisory Committee to OSHA that developed the OSHA ROPS standard. My opposition to authors Karlson and Noren's conclusion is that they say the voluntary standard movement is not working. That is not true. It has worked and I have the statistics to show that it has. My concern with this report is that it will show up in future references alluding that voluntary standards have failed. This is not true. Voluntary standards are a vital part in making agricultural employment safer. Rollin D. Schnieder Extension Safety Specialist Dept. ofAgricultural Engineering Cooperative Extension Service University of Nebraska
Karlson and Noren should be complimented for their study of tractor fatalities which appeared in the February, 1979 issue of the America Journal of Public Health. Agricultural accident problem areas have not gotten their fair share of attention from researchersparticularly when considering the number and severity of the problems that exist. For those not well versed in the areas of agricultural and accident re824
search, words of caution are in order about their study. The authors' failure to define "voluntary safety standards" leads to confusion of the issues involved. Their thesis is that "voluntary safety standards have failed." Yet nowhere in their study do they present evidence that people are being killed because a ROPS was not strong enough, bolts were breaking from anchorage points, etc. Their premise seems to be that people are not voluntarily buying and using enough of the safety equipment being made available and an increasing accidental death rate is the result. That is a meaning far different from that embodied in the term "failure of voluntary safety standards." Much of the authors' conclusion seems to be based on the directional changes noted in the tractor accident death rates. Any of a number of factors could produce this statistical variation and, thus, lead to erroneous conclusions. Collapsing data, interpolation and extrapolation provide opportunities for statistical error and trend distortion to creep in. Changes in the accuracy of determining and reporting cause of death and/or census data could produce interpretation error. And one must question the validity of using an accidental death rate as a means of comparison-deaths per million man hours of tractor use would provide a much more valid comparison. Even if subsequent analyses were to validate the statistical trend, there is little justification to generalize these findings on a national basis. The researcher must keep in mind the tremendous diversity that exists in American agriculture and the rate of machinery replacement. That which is found in Wisconsin-particularly one 4-county area-is but one sample. The researchers' major recommendation for remedial action-that all tractors sold be required to have ROPS installed-might be supportable on an opinion basis and is worthy of consideration. But the authors' apparent failure to consider the practical problems involved with implementing such a recommendation, in addition to basing it on unvalidated, over-generalized data, detracts from any scientific support for such a proposal.
Gary Erisman, PhD Extension Safety Leader Florida Cooperative Extension Service University of Florida Institute of Food and Agricultural Sciences
Authors' Response In Wisconsin, the injury death rate associated with tractors on farms increased from 10.9/100,000 male farm residents during 1961-1965 to 13.6/ 100,000 during 1971-1975 (p < .05). Deaths associated with overturning tractors were most common, with death rates of 6/100,000 male farm residents for 1961-1975. Pfister, Erisman and Schnieder disagree with our conclusion that voluntary safety efforts failed to protect male farm residents from death due to tractor-related in-
juries. Pfister's argument is that increased death rates merely reflect increased exposure to tractors. That may be, however, it does not change the fact that a Wisconsin farmer in 1975 was at greater risk of dying from a tractor-related injury than a farmer in 1961. It is clear that voluntary standards were not adequate to ensure that occupant protection kept up with increased tractor use, or with other risks which may have increased during the time period. Actually, as exposure to an injury- or disease-producing agent increases, the size of the public health problem it presents will increase as well. More exposure to tractors, therefore, argues for, rather than against, the need for improved safety standards. As Erisman points out, our concern is not with the adequacy of the industry-set standards for operator protection, but with their voluntary nature. Manufacturers can choose whether or not to follow the standards and farmers have chosen not to use tractors so equipped in large enough numbers to lower death rates in the population. We stand by our statement: voluntary standards have failed. Erisman is also concerned with our use of death rates per capita. We justify our choice with two reasons: exposure data for Wisconsin do not exist and, furthermore, they are not essential factors in AJPH August 1979, Vol. 69, No. 8
would assume that there are no lives being saved because of ROPS. Yet I know much better since I have information on at least 35 overturn incidents in Nebraska where ROPS were in place and lives saved. This was done as part of the voluntary program in Nebraska and not because of a government requirement. Without ROPS, 40 per cent of the operators of the tractor overturns should have been killed. This figure is taken from a Nebraska overturn study that was started in 1966, 10 years before the OSHA standard came into being. That study has been continued since 1966. I know how the accidents happened since staff of the Department of Agricultural Engineering were involved in researching the site of the tractor overturns. I am familiar with the history of roll over protective structures. The Department of Agricultural Engineering at the University of Nebraska played an important part in the development of ROPS. Also, I served as chairman of the Agricultural Advisory Committee to OSHA that developed the OSHA ROPS standard. My opposition to authors Karlson and Noren's conclusion is that they say the voluntary standard movement is not working. That is not true. It has worked and I have the statistics to show that it has. My concern with this report is that it will show up in future references alluding that voluntary standards have failed. This is not true. Voluntary standards are a vital part in making agricultural employment safer. Rollin D. Schnieder Extension Safety Specialist Dept. ofAgricultural Engineering Cooperative Extension Service University of Nebraska
Karlson and Noren should be complimented for their study of tractor fatalities which appeared in the February, 1979 issue of the America Journal of Public Health. Agricultural accident problem areas have not gotten their fair share of attention from researchersparticularly when considering the number and severity of the problems that exist. For those not well versed in the areas of agricultural and accident re824
search, words of caution are in order about their study. The authors' failure to define "voluntary safety standards" leads to confusion of the issues involved. Their thesis is that "voluntary safety standards have failed." Yet nowhere in their study do they present evidence that people are being killed because a ROPS was not strong enough, bolts were breaking from anchorage points, etc. Their premise seems to be that people are not voluntarily buying and using enough of the safety equipment being made available and an increasing accidental death rate is the result. That is a meaning far different from that embodied in the term "failure of voluntary safety standards." Much of the authors' conclusion seems to be based on the directional changes noted in the tractor accident death rates. Any of a number of factors could produce this statistical variation and, thus, lead to erroneous conclusions. Collapsing data, interpolation and extrapolation provide opportunities for statistical error and trend distortion to creep in. Changes in the accuracy of determining and reporting cause of death and/or census data could produce interpretation error. And one must question the validity of using an accidental death rate as a means of comparison-deaths per million man hours of tractor use would provide a much more valid comparison. Even if subsequent analyses were to validate the statistical trend, there is little justification to generalize these findings on a national basis. The researcher must keep in mind the tremendous diversity that exists in American agriculture and the rate of machinery replacement. That which is found in Wisconsin-particularly one 4-county area-is but one sample. The researchers' major recommendation for remedial action-that all tractors sold be required to have ROPS installed-might be supportable on an opinion basis and is worthy of consideration. But the authors' apparent failure to consider the practical problems involved with implementing such a recommendation, in addition to basing it on unvalidated, over-generalized data, detracts from any scientific support for such a proposal.
Gary Erisman, PhD Extension Safety Leader Florida Cooperative Extension Service University of Florida Institute of Food and Agricultural Sciences
Authors' Response In Wisconsin, the injury death rate associated with tractors on farms increased from 10.9/100,000 male farm residents during 1961-1965 to 13.6/ 100,000 during 1971-1975 (p < .05). Deaths associated with overturning tractors were most common, with death rates of 6/100,000 male farm residents for 1961-1975. Pfister, Erisman and Schnieder disagree with our conclusion that voluntary safety efforts failed to protect male farm residents from death due to tractor-related in-
juries. Pfister's argument is that increased death rates merely reflect increased exposure to tractors. That may be, however, it does not change the fact that a Wisconsin farmer in 1975 was at greater risk of dying from a tractor-related injury than a farmer in 1961. It is clear that voluntary standards were not adequate to ensure that occupant protection kept up with increased tractor use, or with other risks which may have increased during the time period. Actually, as exposure to an injury- or disease-producing agent increases, the size of the public health problem it presents will increase as well. More exposure to tractors, therefore, argues for, rather than against, the need for improved safety standards. As Erisman points out, our concern is not with the adequacy of the industry-set standards for operator protection, but with their voluntary nature. Manufacturers can choose whether or not to follow the standards and farmers have chosen not to use tractors so equipped in large enough numbers to lower death rates in the population. We stand by our statement: voluntary standards have failed. Erisman is also concerned with our use of death rates per capita. We justify our choice with two reasons: exposure data for Wisconsin do not exist and, furthermore, they are not essential factors in AJPH August 1979, Vol. 69, No. 8
