This paper shows how the tools of evaluation methodology can be applied in order to provide the best possible information on the likely outcomes of proposed programs. A prospective evaluation synthesis may be conducted by comparing policy or program alternatives or by focusing on a single policy or program. It is easiest to perform when an adequate data base already exists. Fortunately, data bases concerning proposed programs frequently do exist, primarily because problems are rarely new, and past attempts to address them can be drawn upon for the synthesis. The paper focuses on a systematic method for providing the best possible information to decision makers and techniques for analysing alternative proposals and projections.