U.S. Environmental Protection Agency


Date of this Version



Published in Journal of the American Water Resources Association (2007) 43:2 384-397. DOI: 10.1111 ⁄ j.1752-1688.2007


Multiple agencies in the Pacific Northwest monitor the condition of stream networks or their watersheds. Some agencies use a stream ‘‘network’’ perspective to report on the fraction or length of the network that either meets or violates particular criteria. Other agencies use a ‘‘watershed’’ perspective to report on the health or condition of watersheds. The agencies often use the same indicators and measurement protocols for data collection and often conduct monitoring in overlapping geographic regions. In these situations, agencies would like to combine data across different monitoring studies in a statistically sound manner to make regional estimates of condition. Three statistical survey design principles will facilitate combining such studies: (1) a clearly specified statistical target population of interest, including elements that comprise the population, (2) a consistent representation of that target population (such as a digital map of the stream network and watersheds), and (3) rules that incorporate randomization to guide the selection of the sample of sites on which measurements will be made. A case study illustrates the application of these design principles using two agency monitoring programs interested in combining stream channel data for different purposes: one for making network summaries and the other for evaluating watershed condition.