Quality improvement (QI) attempts to change clinician behavior and, through those changes, lead to improved patient outcomes. The methodological quality of studies evaluating the effectiveness of QI interventions is frequently low. Clinicians and others evaluating QI studies should be aware of the risk of bias, should consider whether the investigators measured appropriate outcomes, should be concerned if there has been no replication of the findings, and should consider the likelihood of success of the QI intervention in their practice setting and the costs and possibility of unintended effects of its implementation. This article complements and enhances existing Users' Guides that address the effects of interventions--Therapy, Harm, Clinical Decision Support Systems, and Summarizing the Evidence guides--with an emphasis on issues specific to QI studies. Given the potential for widespread implementation of QI interventions, there is a need for robust study methods in QI research.