Why does geographic variation in health care practices matter? (And seven questions to ask in evaluating studies on geographic variation).

One of the most active fields in health services research is the study of "geographic variation," or disparities in rates of certain types of health care practices among large areas (such as countries or regions of a country) or small areas (such as countries or hospital market areas); "small area analysis" in particular has received much attention in journals and the popular press. Increasingly, data upon which to base studies of geographic variation are becoming available. This article poses questions to ask in applying studies on geographic variation to health care settings. Because findings from these studies may ultimately affect patient care, the questions are important for physicians as well as health services researchers. The questions are: 1) What events are to be analyzed? 2) What geographic units are to be analyzed? 3) How good are the data? 4) Are differences in rates due to chance alone? 5) Are high rates too high? 6) How is geographic variation to be explained? 7) What is the role of "presentation style" in explaining geographic variation?