Usual source of care: an important source of variation in health care spending.

Health care spending varies in unexplained ways, and physicians' behavior is thought to explain much of the variation. We studied the spending effects of having different usual sources of care, focusing on variations associated with the type of facility or physician specialty. Based on analyses of data from the 2001-2004 Medical Expenditure Panel Surveys, we found significant differences in annual spending, especially for adults. Use of and spending for subspecialists were similar to those for general internists, and both were significantly higher than those for family physicians. Variation in spending might be the result of training differences among primary care specialties.