rough consensus on the best way to handle particular types of cases, but that their consensus differs from the next community and will produce care patterns that are stunningly different from those in other communities, even within the same state or region. For a quick introduction, start with the Dartmouth Medical Atlas , published by the Center for Clinical Evaluative Studies, which is one of the offshoots of Wennberg's work. These variations also exist within similar populations and in some cases very homogeneous populations. For example, a colleague studied variation in hospitalization patterns among Nebraska Blue Cross subscribers for conditions that can be managed on an outpatient basis (diabetes, asthma, CHF, COPD, etc.) As another example, in the late 1980s and early 1990s, my own work focused on variation in hospitalization patterns of Medicaid clients in New York. Here's a quick and dirty update that I did in 2003 . The earlier work was much more rigorous and I'll be happy to send a copy to anyone who asks. Wennberg and his followers also learned that the variation itself varies from one condition to another. For example, appendectomies are always performed in hospitals and there is no known relationship of appendicitis to age, gender, race, socio-economic status. So there is very little variation and, from what I've seen, it's just random. Other conditions, however, are quite different. For just a tiny sample take a look at these: Regional variation in medical care , NEJM, August 31, 1995 where Detsky noted