In the 1990s, evidence-based medicine emerged as a way to improve and evaluate patient care. It involves combining the best research evidence with the patient's values to make decisions about medical care. Looking at all available medical studies and literature that pertain to an individual patient or a group of patients helps doctors to properly diagnose illnesses, to choose the best testing plan, and to select the best treatments and methods of disease prevention. Using evidence-based medicine techniques for large groups of patients with the same illness, doctors can develop practice guidelines for evaluation and treatment of particular conditions. In addition to improving treatment, such guidelines can help individual physicians and institutions measure their performance and identify areas for further study and improvement. The February 25, 2009, issue of JAMA includes an article about the importance of using evidence-based medicine to develop practice guidelines. This Patient Page is based on one published in the September 6, 2006, issue of JAMA.