as part of a program to improve community health. The village had no electricity or water distribution system so villagers got water directly from a stream. Students working on this project examined the quality of the filters by looking at many different variables, including: general observations, filter observations, microbiology observations, household practice observations, user perceptions, and water source observations. When making inferences, the water filters considered are a sample of all filters that could be constructed if this pilot project were expanded to other villages. Thus, inference is to an as-yet-unbuilt, larger population of filtersWhat are the observational units