The excellent Steve Sisson sent me that. The article is by Luisa Franzini, Osama I. Mikhail, and Jonathan S. Skinner. Here is the abstract:
Medicare spending for the elderly is much higher in McAllen, Texas, than in El Paso, Texas, as reported in a 2009 New Yorker article by Atul Gawande. To investigate whether this disparity was present in the non-Medicare populations of those two cities, we obtained medical use and expense data for patients privately insured by Blue Cross and Blue Shield of Texas. In contrast to the Medicare population, the use of and spending per capita for medical services by privately insured populations in McAllen and El Paso was much less divergent, with some exceptions. For example, although spending per Medicare member per year was 86 percent higher in McAllen than in El Paso, total spending per member per year in McAllen was 7 percent lower than in El Paso for the population insured by Blue Cross and Blue Shield of Texas. We consider possible explanations but conclude that health care providers respond quite differently to incentives in Medicare compared to those in private insurance programs.