Through the use of specific examples to illustrate evaluation research goals and methods, this book provides readers with an overview of the science and politics of evaluation research that is comprehensive in the topics covered, but selective in the details discussed. The Second Edition includes coverage of meta-analysis, selection models and instrumental variables. In addition, the authors have expanded their sections of the analysis of data, evaluation when the units of analysis are entire organizations or political jurisdictions, and comparisons between evaluation research and other fields.