No studies with survey data were conducted from a population-based random sample of this magnitude before or since the 2002 study documenting both fatal and nonfatal injuries associated with tractor overturns. Study limitations are noted below. Finally, the application of the study findings are discussed, and the prevalence of non-ROPS tractors is considered in some countries experiencing increasing agricultural machinery mechanization.
Six limitations are described below: three regard the underreported number of fatal and nonfatal injuries, a fourth addresses the issue of exposure measurement, another discusses the current relevance of the 14-year-old study, and a sixth describes the generalizability of the results to a broader population.
First, the healthy worker effect may cause underreporting [27
]. Farmers’ whose operations went out of business because of a severe or fatal tractor overturn injury were removed from the NASS state and national list of farm operations. During the approximate 41-year period spanned by the survey, the overturn events were those reported by healthy farmers, or by the family members of injured or deceased farmers’ whose operations remained in business and were, therefore, included in the Kentucky NASS 2001 comprehensive farm list. Thus, data for nonfatal and fatal tractor overturn events from farm operations no longer in business were not counted.
Second, the number of overturn injuries and fatalities reported includes only each farm’s most recent tractor overturn event of Kentucky’s 75,780 farms at the time of the survey. One item at the beginning of the survey asked farmers to report the total number of all tractor overturns that had occurred in the history of their operation. A total of 551 farms reported 603 overturns during the history of their operation. However, to minimize the response burden for the farmers, and to help ensure accuracy of reporting, each farm operator was asked to report only the details for their most recent tractor overturn event. Thus, details for these additional 52 overturn events were not collected.
Third, the survey included only a 7.98% random sample of Kentucky farmers for an approximate 41-year period, As a consequence the total number of fatal and nonfatal tractor overturns within the Kentucky farm operator population over the period are 12.5 times greater than those identified by the survey. Even so, the survey results are robust and useful because they are based on a large statewide, population-based random sample stratified by farm size and USDA agricultural district.
Fourth, while this study addresses qualitative exposures (i.e., exposures to chores), quantitative exposure data would be useful for similar studies. These exposure data could better indicate priorities for educational or ROPS retrofit programs. However, the challenge for measuring exposure is problematic: (1) recall is a problem, especially considering the use of multiple tractors on a farm over a long period of time; and (2) tractor meters are a source of engine running time, but the meters do not differentiate between stationary and mobile operations, and the meters may become defective over time or by damage.
Fifth, this analysis is based on a study conducted 14 years ago in 2002, and the relevance of its results might be questioned. In a 2008 study, investigators found that non-ROPS prevalence on farm tractors in the United States decreased from 62% in 1993 to 54% in 2001, and to 49% in 2004. In 2004, there were 4 million tractors in the United States [28
]. A 2010 study found that, by 2006, the non-ROPS prevalence had dropped to 41%. Over the period, from 1992 to 2007, tractor overturns accounted for 1412 deaths, and for each 1% decrease in non-ROPS tractor prevalence, there was a decrease of 0.07 overturn-related deaths per 100,000 workers [2
]. The non-ROPS tractors reported in the current study are the same older tractors reported in the 2008 and 2010 studies. Nearly two million non-ROPS tractors manufactured prior to 1985 remain in service and a threat to life today [12
Sixth, the current study was conducted in the state of Kentucky, so generalizability might be questioned. This data have been found to be generalizable to the non-ROPS problem in the high risk areas of the United States [24
]. Another study, using the same dataset, found that Kentucky and five other nearby states had the highest fatality rate regarding overturn-related deaths among all 50 states in the country. These six states have rugged terrain and small farms in common [29
]. Indeed, another study using the same data set affirmed that rough terrain was typical of small farms in the Appalachian Mountains’ foothills that had a higher tractor overturn rate than large farms on relatively level ground [25
This study provided detailed information about the frequency, type, and extent of injuries associated with non-ROPS and ROPS-equipped tractor overturns across an array of chores. Data about these chores and other variables provide information about EMT received, hospital admission rates, days in the hospital, days of work lost, and disability outcomes and their duration. These data are useful in at least three ways.
First, the data can be used to provide more accurate estimates of the costs of tractor overturn injury outcomes as related to the chore performed, as well as for calculating cost effectiveness estimates for preventing injuries. For example, differentiating the potential cost savings of injuries prevented for crop-type chores (e.g., mowing) relative to livestock-type chores (e.g., fence work) would help to counter the averaging effect in cost analyses for ROPS retrofit interventions. As described earlier, ROPS-equipped tractors are less prevalent on crop farms than livestock farms [2
]. Thus, a cost savings case could potentially be made for targeted education and ROPS retrofit programs and retrofitting tractors used for crop farming where the overturn-related injury risk is higher and the potential benefit is higher.
Second, the results can be used to design educational materials and interventions. These can be used to inform farmers and others who have a stake in preventing tractor-related injuries about the circumstances and details of chores that result in tractor overturn injuries and methods for their prevention.
Third, this study reinforces the need to encourage retrofitting older tractors with ROPS. Four overturns involving ROPS-equipped tractors resulted in nonfatal hospital admissions—however, none resulted in permanent disabilities.
4.3. Non-ROPS Tractors in Countries with Emerging Mechanization
Economically-challenged small farms and rough terrain, including unpaved roadways, are present in Kentucky [30
] as well as in other countries such as China and India. While farm mechanization has come late to many countries, there is emerging interest regarding tractor overturning incidents and safety [31
]. Tractors are coming into increased use in these countries, and they typically lack ROPS protection. India and China have numerous tractor manufacturers. Major tractor manufacturers in India include Escorts, Crossword Agro Industries, Mahindra Gujurat Tractor Limited, Punjab Tractors Ltd. (Swaraj), and MARS Farm Equipment Ltd. In India, tractors are a common mode of road transport in rural areas and often involve multiple riders per tractor [32
]. Based upon product lines viewed at the webpages of these companies, none of the models shown were equipped with ROPS. China has more than 60 companies that manufacture tractors, which vary from 1960s technology to modern designs. Some of these companies have partnered with international companies, such as John Deere and AGCO [33
]. One company that manufactures tractors in China, Wuzheng Agricultural Equipment Co., shows 94 tractor models on its website, 38% with cabs (whether ROPS outfitted or not), 2% fitted with a roll bar, and 60% with no ROPS [34
The lack of ROPS on these tractors can be expected to result in the same tragedies that continues to be experienced in some highly mechanized countries despite the knowledge of the protection provided by ROPS. Regarding chores, studies need to be conducted in these countries to better understand risks associated with tractor overturns. While a tractor is likely the only motorized vehicle operating on a farm, its broader use as a utility vehicle (e.g., people transport) needs to be better understood so as to guide priorities for education and, more importantly, fitting the tractors with rollover protection.