The evidence related to health care delivery, organization, and financing often describes complex systems processes. Without clearly stated definitions of the processes of interest, it can be difficult to identify the research questions, develop appropriate literature searches, and formulate inclusion and exclusion criteria. Thus, for some projects, the essential task of the problem formulation stage is the defining of relevant concepts. For example, in the review “Measures of Patient Safety Based on Hospital Administrative Data: The Patient Safety Indicators,” the authors evaluated patient safety indicators developed from administrative data (9). They began by developing a set of standardized definitions of 9 key concepts relevant to their topic, including quality of health care, quality indicators, patient safety, patient safety indicators, medical error, and adverse events (9). They used these definitions to develop a list of potential indicators of medical errors, patient safety, or potentially preventable complications (9). The authors then invited 21 professional clinical organizations and 16 surgical subspecialty organizations to submit nominations of experts to evaluate potential patient safety indicators. An expanded expert advisory group of 76 clinicians (divided into 11 panels) reviewed and evaluated indicators according to a method adapted from the RAND/UCLA Appropriateness Method (23). This consisted of an initial independent assessment of each indicator by clinician panelists using an initial questionnaire, a conference call among all panelists, followed by a final independent assessment by clinician panelists using the same questionnaire (9). The panel process served to refine definitions of some indicators, add new measures, and dismiss indicators with major concerns from further consideration (9). Finally, a subset of 34 of the most promising indicators was developed and additional literature was sought for studies describing these indicators. This unique use of a series of expert advisory panels produced inclusion criteria with considerable face validity given the breath and depth of the clinical specialists involved in the process.