Intervention studies and the definition of dominant transmission routes.

A common approach to assessing the relative importance of different transmission routes is to eliminate transmission through one route and assume that the ratio "number of cases eliminated:number of residual cases" measures the relative importance of the eliminated route vis-à-vis the residual transmission route. A quantitative model is used to generate synthetic data similar to those analyzed by epidemiologists. These data are analyzed using this conventional procedure and the inferences drawn from the synthetic data compared with the causal relationships structured into the model. The implications for the analysis of real-world data are analyzed by examining data on the importance of water and other transmission routes for cholera in Bangladesh.