When Dartmouth economics professor Jonathan Skinner was speaking recently at the University of Texas about the "cowboy doctor" problem, an audience member objected: "You have a problem with cowboys?" Well, actually, we all have a problem with cowboys — when they're doctors. Including the Texans. New research written up in a National Bureau of Economic Research paper finds that "cowboy" doctors — who deviate from professional guidelines, often providing more aggressive care than is recommended — are responsible for a surprisingly big portion of America's skyrocketing health costs. The paper concludes that "36 percent of end-of-life spending, and 17 percent of U.S. health care spending, are associated with physician beliefs unsupported by clinical evidence."