We often decide what to believe and what to question on the basis of a simple rule of thumb like believe the trustworthy source or trust the expert. Sometimes, however, reliable and well-informed sources support both sides of the controversy. Whom are we to trust? How can we make a decision on the issue at hand? The second edition of Evaluating Social Science Research provides methods for thinking critically about claims of factual knowledge and drawing appropriate conclusions. The authors have added new sections to the book to reflect the new developments in the field since the appearance of the first edition sixteen years ago. Included is an expanded discussion of observational method that addresses the issues of validity that are now more clearly understood. There is an explicit discussion of quasi-experimental research design, including an added distinction between equivalent-group and nonequivalent-group experiments. New explanations of the logic of multiple regression analysis, casual modeling, and meta-analysis have been provided as well. The new edition, while recognizing the limits of each research method, retains its emphasis on the importance of observations that may be repeated and checked by other researchers. It treats the reader as a key actor who can advance knowledge by cross-checking observations and interpretations.