Relative Extent, Relative Risk and Attributable Risk Calculations

Official websites use .gov
A .gov website belongs to an official government organization in the United States.

Secure .gov websites use HTTPS
A lock () or https:// means you’ve safely connected to the .gov website. Share sensitive information only on official, secure websites.

This is not the current EPA website. To navigate to the current EPA website, please go to www.epa.gov. This website is historical material reflecting the EPA website as it existed on January 19, 2025. This website is no longer updated and links to external websites and some internal pages may not work. More information »

JavaScript appears to be disabled on this computer. Please click here to see any active alerts.

Relative Extent, Relative Risk and Attributable Risk Calculations

National Aquatic Resource Surveys