For 305(b) reports, I need to estimate the total number of stream miles in my EPA Region that are degraded. Can I do this from sample survey data?
The number of degraded stream miles can be calculated in two steps. First, the proportion of stream miles that are degraded is calculated as illustrated earlier. Then, that fraction is multiplied by the total number of stream miles in the population. The total number of stream miles is available from the sampling frame (for example from EPA s River Reach File, Version 3), which delineates all members of the target population. Defining “degraded” is an important part of the calculation, regardless of whether it is for percent or absolute number of stream miles. “Degraded” can be defined if a threshold value or goal for each measurement variable can be established. Most of the variables measured in stream surveys, such as an Index of Biotic Integrity (IBI), have continuous ranges of response. Calculating the proportion of stream miles that are degraded requires converting this continuous data into binary, or yes/no (e.g., degraded or not degraded) form. The question of how many stream mi
