For both human health and ecological risk assessments, EPA implements a tiered approach, beginning with a screening analysis and moving, as warranted, to more detailed analyses. The screening analysis uses existing data, defined decision criteria and models with simplifying, conservative assumptions as inputs. By using these default assumptions, EPA ensures that a lack of data does not result in overlooking a source category that may pose significant risk. A more refined analysis requires more resources and data, but the results are more certain and less likely to overestimate risk. EPA also conducts demographic analyses to better understand the potential impacts of the rule on low income, minority or indigenous communities.