Random assignment experiments are widely used to test the effectiveness of new social interventions. Part of MDRC's methodology work paper series, this paper discusses several major welfare-to-work experiments, highlighting their evolution from simple "black box" tests of single interventions to multigroup designs used to compare alternative interventions or to isolate the effects of components of an intervention. The paper also discusses new efforts to combine experimental and non-experimental analyses in order to test underlying program theories and maximize the knowledge gained about the effectiveness of social programs.

This is part of a series of MDRC working papers that explore alternative methods of evaluating the implementation and impacts of social programs and policies.

Work on the paper was supported by a grant from The Rockefeller Foundation to further a U.S.- U.K. dialogue on evaluation research, a grant from the Pew Charitable Trusts to promote the development of new quantitative and qualitative evaluation research methodologies, and a grant from the Russell Sage Foundation to prepare a book on combining experimental and nonexperimental methods for measuring the impacts of social programs.