Thousands of doctors and other medical professionals have steadily billed higher rates for treating elderly patients on Medicare over the last decade—adding $11 billion or more to their fees and signaling a possible rise in medical billing abuse, an investigation by the Center for Public Integrity has found. The Center's analysis of Medicare claims from 2001 through 2010 shows that over time, thousands of providers turned to more expensive Medicare billing codes, while spurning use of cheaper ones. They did so despite little evidence that Medicare patients as a whole are older or sicker than in past years, or that the amount of time doctors spent treating them on average was rising.