... incomplete, as is often thecase, assumptions based on scientific judgments are made to calculate potentialexposures and effects. Specifically, when direct observations of the effects of environmental ... identify diseases related to chemicals in theenvironment. Systematic collection of such data in disease registries can help toidentify unusual clusters of deaths, cases of disease, or cancers ... important. Areas that must beaddressed include the nature of the problem, the objectives of the study, thedefinition of the event and unit of observation, characterization of the system,sources of data,...