Nearly 130 million visits to emergency departments (EDs) occur every year in the United States (1). Whether patients should have gone to the ED in the first place is frequently debated, because the ED is often viewed as an overcrowded, overused, misused, and costly resource. Yet patients rarely present to the ED for unnecessary reasons (2). Judging appropriateness of ED visits often suffers from hindsight bias or misapplication of methods to judge appropriate use (2–4). Although emergency care may be more expensive than office-based care, when the populations served, patient complexity, 24/7 access, and proportion of total healthcare costs are considered, emergency care adds value, and would be costly to replace (5). Yet there remains ample room to improve the acute care for many conditions. One critical area of focus is on whom to admit versus discharge. Although only 13.3% of U.S. ED patients were admitted in 2010, the ED is the source of more than one-half of hospital admissionsdthe most expensive resource in healthcare (1,6).