Deciding which pathways to consider in a causal assessment—that is, listing candidate causes as described in Step 2 of the SI process—sets the framework for causal assessment. This section of CADDIS provides background information on commonly encountered sources, stressors, and responses for use in deciding which candidate causes to consider, as well as in developing cases for or against those candidate causes in the actual assessment.

Each stressor module is organized into five sections, or tabs:

• Introduction provides a summary overview of the stressor, including a checklist of evidence that suggests including a given stressor in your assessment (i.e., listing it as a candidate cause).
• When to List provides more detailed information on the sources, activities, site evidence, and biologial responses that suggest inclusion as a candidate cause.
• Ways to Measure details different methods for quantifying the stressor.
• Conceptual Diagrams illustrates hypothesized causal linkages among the stressor, its sources, and associated biotic responses.
• References lists the references cited throughout the module.

In addition, some stressor modules have a Literature Reviews tab, which presents an annotated bibliography of key references providing general background information, particularly regarding stressor-response relationships.

The source module for urbanization contains similar summary information on effects of urban development on stream ecosystems, but it is presented in a different format. The module is organized using a simple schematic of how urbanization affects streams. Users can click on any shape in the schematic to navigate through the module and focus on areas of interest; within each section (i.e., under each shape) the user can click on additional topic boxes for more detailed information.