How epidemiology can help produce better health policy. Although policy is not necessarily (or perhaps not ever) developed in a logical sequence, it is helpful to present the contribution of epidemiology to each stage of an idealized policy cycle. The cycle used here is not original, but is derived from similar cycles presented in textbooks of planning; it bears a particular debt to the Iterative Loop of Tugwell et al , which is presented in a language that is much more familiar to epidemiologists than that used in the social science literature (see next slide)