Evaluators and applied researchers who want to enhance their understanding of research design and of threats to valid inference will find this book an effective guide. The First Edition was popular for its integration of multiple regression with evaluation desig, and for offering systematic ways to select the proper goals for single- and multiple-outcome evaluations. This edition has been revised to cover new issues and to clarify further the concepts used in impact analysis. New features include: expanded coverage and explanation of quasi-experiments; a section on impact analysis theory; a section on the use of qualitative research for impact analysis; expanded coverage of significance testing for programme evaluation; an explanation of why the comparative-change design is better than an ex-post-facto design from the standpoint of causal inference; a clarification of the effects of volunteering or self-selection; and a new simplified appendix on regression artefacts.