Reproducibility of reported farming activities and pesticide use among breast cancer cases and controls: A comparison of two modes of data collection

PURPOSE: Farming is associated with exposure to many potential hazards incl uding pesticides and other agents, but the quality of self-reported data on farm exposures has not been well studied. METHODS: The reproducibility of self-reported farming history was evaluated among women in a population-based, case-control study of breast: cancer in North Carolina. Thirty cases and 31 controls were randomly re-interviewed by telephone an average of 13.8 months after the initial interview. The ini tial interview was based on a farm-by-farm questionnaire, while the repeat interview was based on a shorter ever/never questionnaire. Agreement was es timated using proportions in exact agreement, kappa (kappa), and intraclass correlation coefficients (ICC). RESULTS: In general, group prevalences and means were higher on re-intervie w. Kappa estimates ranged from 0.15 to 0.84 among cases, and 0.26 to 0.87 a mong controls, with most estimates falling between 0.5 and 0.8. Moderate to almost perfect agreement (kappa) was observed for questions on crop work ( 0.47-0.70), crop type (0.56-0.82), pesticide application to tobacco (0.77), and farm residence (0.84). ICC estimates for continuous variables showed f air to substantial agreement (0.30 to 0.69 among cases, 0.38 to 0.69 among controls). Cider cases, less educated cases, cases who lived on more than o ne farm, and cases with longer time intervals between interviews gave lower total agreement than similar groups of controls. CONCLUSIONS: Agreement estimates in this study are similar to those for oth er types of exposure information typically collected in epidemiologic studi es. Nevertheless, a farm-by-farm method of exposure assessment may he prefe rable to an ever/never determination.,Ann Epidemiol 2001;11:178-185. (C) 20 01 Elsevier Science Inc. All rights reserved.