Is farm-related job title an adequate surrogate for pesticide exposure in occupational cancer epidemiology?
- 1Monash Centre for Occupational and Environmental Health, Department of Epidemiology and Preventive Medicine, Monash University, Melbourne, Australia
- 2Western Australian Institute for Medical Research, Sir Charles Gairdner Hospital, Perth, Australia
- Ewan MacFarlane, Monash Centre for Occupational and Environmental Health (MonCOEH), Department of Epidemiology and Preventive Medicine, Faculty of Medicine, Nursing and Health Sciences, Monash University, The Alfred Hospital, Commercial Road, Melbourne, Victoria 3004, Australia;
- Accepted 24 October 2008
- Published Online First 15 February 2009
Objectives: Accurate assessment of exposure is a key factor in occupational epidemiology but can be problematic, particularly where exposures of interest may be many decades removed from relevant health outcomes. Studies have traditionally relied on crude surrogates of exposure based on job title only, for instance farm-related job title as a surrogate for pesticide exposure.
Methods: This analysis was based on data collected in Western Australia in 2000–2001. Using a multivariate regression model, we compared expert-assessed likelihood of pesticide exposure based on detailed, individual-specific questionnaire and job specific module interview information with reported farm-related job titles as a surrogate for pesticide exposure.
Results: Most (68.8%) jobs with likely pesticide exposure were farm jobs, but 78.3% of farm jobs were assessed as having no likelihood of pesticide exposure. Likely pesticide exposure was more frequent among jobs on crop farms than on livestock farms. Likely pesticide exposure was also more frequent among jobs commenced in more recent decades and jobs of longer duration. Our results suggest that very little misclassification would have resulted from the inverse assumption that all non-farming jobs are not pesticide exposed since only a very small fraction of non-agricultural jobs were likely to have had pesticide exposure.
Conclusions: Classification of all farm jobs as pesticide exposed is likely to substantially over-estimate the number of individuals exposed. Our results also suggest that researchers should pay special attention to farm type, length of service and historical period of employment when assessing the likelihood of pesticide exposure in farming jobs.
Funding: The original case–control study on which the analyses in this paper are based was funded by Healthway and the BUPA Foundation. Ewan MacFarlane is supported by an NHMRC Postgraduate Research Scholarship. Lin Fritschi is supported by an NHMRC fellowship.
Competing interests: None.