A program's effect can be measured accurately only if one knows what would have happened without it. Because one obviously cannot observe the outcomes for the participants themselves had they not enrolled in the program, a proxy group of nonparticipants must be identified. Determining this hypothetical no-treatment (or counterfactual) state is the crux of designing an evaluation. Evaluation designs are categorized according to the way in which the counterfactual group is selected -nonrandom assignment (classified as a quasi-experimental design) and random assignment (classified as an experimental design). In the quasi-experimental category the two principal types of design are reflexive techniques, in which the postprogram behavior of participants is compared with their preprogram behavior, and matched comparisons, in which the postprogram behavior of the participants is compared with the behavior of a group of individuals who were similar to the participants before they enrolled in the program. The paper discusses the relative advantages and disadvantages of each evaluation design in different situations, and describes the experience accumulated in the United States in applying them in practice. Choosing an evaluation method depends on the kinds of questions being asked about a program, the number of participants the program will serve, the operational details that might make one or another type of evaluation unsuitable, and the constraints on the time and resources available for the exercise.
Bibliography: Grossman, Jean Baldwin. 1994. "Evaluating Social Policies: Principles and U.S. Experience." The World Bank Research Observer, vol. 9, No. 2 (July 1994), pp. 159-80. World Bank, Washington, DC.
