CADDIS Volume 3: Examples & Applications


Notice - This site contains archived material(s)

Archive disclaimer
Archived files are provided for reference purposes only. The file was current when produced, but is no longer maintained and may now be outdated. Persons with disabilities having difficulty accessing archived files may contact the NCEA Webmaster for assistance. Please use the contact us form if you need additional assistance.


This project provides the development plan for a decision support system that encompasses guidance, case studies and analytical tools that will help scientists in states and regions in identifying causes of biological impairments in aquatic ecosystems.

Project Status

The Stressor Identification Guidance Document was published in December 2000 (EPA/822/B-00-025). A workshop on the development of the system was convened in August 2002: the final report is available (see related entries). A report describing the plan for developing the Causal Analysis/Diagnosis Information System was published in January 2004.

Project Start Date


Project Completion Date (Actual/Projected)



The Causal Analysis/Diagnosis Decision Information System (CADDIS) is a web-based system that provides technical support for states, tribes and other users of the Office of Water's Stressor Identification Guidance. The Stressor Identification Guidance provides a rigorous and scientifically defensible method for determining the causes of biological impairments of aquatic ecosystems. It is being used by states as part of the TMDL process and is being applied to other impaired ecosystems such as Superfund sites. However, because of the complexity of causal relationships in ecosystems, and because the guidance includes a strength-of-evidence analysis which uses multiple causal considerations, the process is complex and information intensive. CADDIS helps users deal with that inherent complexity.

Increasingly, the regulatory, remedial, and restoration actions taken to manage impaired environments are based on measurement and analysis of the biotic community. When an aquatic assemblage has been identified as impaired, an accurate and defensible assessment of the cause can help ensure that appropriate actions are taken.

The U.S. EPA's Stressor Identification Guidance describes a methodology for identifying the most likely causes of observed impairments in aquatic systems. Stressor identification requires extensive knowledge of the mechanisms, symptoms, and stressor-response relationships for various specific stressors as well as the ability to use that knowledge in a formal method for causal analysis.

The development plan attached below describes a strategy for developing the Causal Analysis/Diagnosis Decision Information System (CADDIS). The CADDIS system is envisioned as a decision support application that will help investigators in EPA Regions, states, and tribes find, access, organize, and share information useful for causal evaluations in aquatic systems.
CADDIS will include supporting case studies and analysis tools, and it will provide access to databases that contain information useful for causal evaluations. The system will be developed incrementally and iteratively with frequent user input and feedback essential to the system's success.


The first version, CADDIS I, leads the user through the process, explains the steps, provides worksheets for completing the steps and illustrates each step using examples from a real case study. CADDIS I was released at the end of CY05.

In 2006, work had begun on CADDIS II, to provide more technical support including a conceptual model library, exposure-response information for common stressors, statistical tools for analyzing state monitoring data and links to data bases. CADDIS II is an ORD-wide effort, which will be completed in 2007.

CADDIS III, which is scheduled for 2009, will contain additional technical support and connectivity to resources that will help users determine the causes of biological impairments.