A methodological study in Iowa was conducted to compare information on agricultural factors obtained by interview from farmers and their proxy respondents. In-person interviews were sought from 100 farmer â€“ surrogate pairs and obtained from 85 pairs. Respondents provided information on farm commodities produced, details on pesticide use, and pesticide application practices. The sensitivity and specificity of surrogate responses were over 90% for information such as years operating a farm or amount of corn or livestock production in recent years. Accuracy was lower for individual pesticides used and details about pesticide application practices (sensitivities from 40 to 70% and specificities from 50 to 90%). Surrogate respondents were unable to provide as much information and reported lower prevalence of pesticide use than the farmers themselves. The correlation between prevalence of individual pesticides reported by farmers and by surrogates was 0.91 for herbicides and 0.78 for livestock insecticides. The loss of information from using proxy respondents would typically bias estimates of relative risk downward toward the null value and could result in false negative interpretations. Although use of surrogates undoubtedly introduces misclassification of agricultural exposures, the degree of misclassification is generally in the range observed for other factors obtained by interview in epidemiologic studies such as information on diet and details of tobacco and alcohol use.
Full article can be found in: Journal of Agricultural Safety and Health
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