What drives our choices? Evidence, guidelines or habit?

Physicians' treatment choices are influenced by a number of factors, including guidelines, evidence-based medicine, past experience and, to a certain extent, habit. Evidence-based medicine is the foundation of clinical practice guidelines. This article reviews the influence of evidence and guidelines on physicians' treatment choices. As examples, the role of evidence in guiding treatment decisions in chronic obstructive pulmonary disease is explored, and the impact of guidelines on treatment choices in community-acquired pneumonia is discussed. When choosing the most appropriate treatment for a patient, physicians need to continuously evaluate new evidence, in addition to implementing clinical practice guidelines. Additional factors that should also influence this decision are physicians' prior experience and the individual patient's circumstances.