Social Impact (SI) is conducting an impact evaluation of the MCC Tanzania Water Sector Project. The impact of the WSP will be assessed through a rigorous, quasi-experimental impact evaluation design that combines a difference-in-differences (DD) approach with generalized propensity score matching (GPSM), also called continuous propensity score matching. GPSM is an extension of traditional propensity score matching which facilitates the evaluation of the impact of continuous rather than binary treatment. The design reflects particular characteristics of the Tanzania WSP. First, the impacts of the upgraded water infrastructure are expected to be diffuse in each city; therefore, identifying a counterfactual through experimental methods is not feasible. Further, the main treatment is considered to be exposure to an increased supply of water due to the Water Sector Project infrastructure upgrades, and households will be affected differentially depending on their starting conditions (e.g. availability of water) and their position along the distribution grid. Thus, a continuous treatment approach is needed to measure the impacts of incremental increases in water supply. The GPSM technique (which will be carried out after the completion of end-line data collection) enables comparisons of outcomes between similar households that experience varying levels of improvements to water supply due to the intervention. The evaluation questions to be answered address a range of topics, including: the project's impact on water supply, access to water, and water quality; the project's impact on water consumption, water-related illness, and investment in human capital; differences in project impact by gender and socioeconomic status; the project's effect on businesses, schools, and health centers; project implementation; unintended consequences of the project; and the sustainability of the project over time. In addition to the main analysis described above, additional qualitative, direct observation (e.g. water quality tests), secondary data review, and geospatial data collection components were incorporated to facilitate comprehensive, context-specific responses to these evaluation questions.
