Statistical techniques applied to environmental health sciences

National Institute Of Environmental Health Sciences

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Abstract

We have recently guided the data analysis for several projects, primarily involving data from the Agricultural Health Study (AHS), a cohort of licensed pesticide applicators (mostly farmers) from Iowa and North Carolina. One project probed a possible relationship between pesticide exposure and depression among male private applicators in the AHS. We used inverse probability weighting to account for exclusions due to missing data and polytomous logistic regression to estimate odds ratios. Ever use of fumigants as a class and several individual pesticides were associated with depression. Using data from the AHS, we have also studied whether farming exposures contribute to exacerbation of asthma. We noted inverse association of asthma with several farming activities and with ever use of two herbicides but no positive associations (except in a subset of cases with asthma and allergy). These observations are consistent with the possibility that asthma cases prone to exacerbation tend to avoid exposures that trigger symptoms. Farmers have different respiratory exposures and, consequently, different respiratory risks than the general population; yet few studies have been able to compare farmers with a corresponding general population. We compared the prevalence of self-reported respiratory outcomes for participants in the AHS with data from adults who participated in the National Health and Nutrition Examination Survey (NHANES) over the same time period. Farmers in the AHS had lower prevalence of respiratory diseases such as asthma, chronic bronchitis, and emphysema but higher prevalence of respiratory symptoms such as wheeze, cough, and phlegm compared to NHANES adults after controlling for smoking and other characteristics that differed between the two populations. Investigation of other aspects of the epidemiology of respiratory disease and symptoms in relationship to farming exposures, including pesticides, is continuing. A last project using data from the AHS examined the possible relationship between diabetes and ever use of specific pesticides before enrollment. Using age as the time scale and diagnosis with diabetes as the event of interest, we fit Cox proportional hazards models to estimate hazard ratios. Ever use of five pesticides (three of them organophosphates) were associated with diabetes among farmers wives who reported ever mixing or applying pesticides.