AHRQ series on PCMH research methods: The patient-centered medical home (PCMH) is a promising model for organizing care to improve quality and accessibility and reduce costs. To refine the PCMH model, evaluators and researchers need methods that yield robust evidence. The PCMH Research Methods Series, funded by the Agency for Healthcare Research and Quality (AHRQ) and developed by Mathematica Policy Research, is designed to “expand the toolbox” of methods used to evaluate PCMH models and other health care interventions. Each of the ten briefs in the series describes a research method, outlines advantages and limitations, and lists resources for researchers to learn more. The topics cover both “evolutionary” ways to improve evaluations—by using traditional research methods—and “revolutionary” approaches that draw on methods from anthropology, organizational analysis, engineering, and political science. The goal is to ensure that evaluations focus not only on “Does it work?” but also on “How does it work?” For example, Efficient Orthogonal Designs describes a tool for use at the outset of a study to compare the effectiveness of different ways of deploying each PCMH component, as well as how the effects of individual components interact. The series is available on the AHRQ Web site at pcmh.ahrq.gov.