Both SIA and ER participate in movements to scientize public policy. They address the questions of what public action can accomplish and whether such action is desirable. Both programs have developed in the face of political confrontations over whether governmental actions work and are cost effective. However, SIA reaches beyond the ambit of ER in two ways. Structurally, it goes beyond the domain of essentially public projects and their effects to include essentially private projects having significant public components. Methodogically, SIA attempts to assess effects realized only in the future, while ER's evaluations concern mainly past and ongoing projects. The bulk of problems is due to political pressures that affect scientific concerns. To deal with them, SIA must understand and accept this combination. Methodological issues (categories of effects, data collection, measurement and validity, inference, projection, and modeling), and political issues (relationship between scientists and citizens, and between scientists and employers, and social structural relationships) are discussed and solutions suggested. Footnotes and approximately 40 references are included.