A historical cohort study of cancer among urban vs. rural residents and farmers vs. non-farmers in Iowa
The aims of this study were to 1) Calculate and analyze "smoking-related" cancer incidence by urban vs. rural residents and farmers vs. non-farmers for 1977-1992; 2) Calculate and analyze incidence rates for the "farming-related" cancers by farmers vs. non-farmers (only males) for 1977-1992, and 3) Evaluate variations between urban and rural residents and farmers and non-farmers in lifestyle (consumption of tobacco and alcohol). Data were used from two previously conducted population-based case-control studies. These studies were "Case-Control Study of Cancer and Drinking Water Contaminants" and "Iowa Portion of the National Collaborative Bladder Cancer Study". Statistically significant findings include: 1) The percentage of current smokers and ex-smokers in urban areas exceeded those in rural areas, males and females in urban areas smoked more cigarettes and consumed more alcohol on a per day basis, and men smoked more and drank more alcohol per day than females; 2) Urban-rural differences of SIR (total observed events in a population/ total expected events in a population) were significant for smoking related cancers as a group, due in part to higher rates of smoking and drinking in urban residents; 3) The risk of smoking-related cancers was significantly greater in non-farmers than in farmers. Completion of this study demonstrated the feasibility of doing a cohort study by linking multiple, distinct, yet complimentary databases. The resulting database is a unique resource for additional studies of cancer. These results have provided preliminary data to support grant proposals to federal agencies to conduct further investigations.