Race and place of residence can have a staggering impact on the course and quality of the medical treatment a patient receives, according to new research showing that blacks with diabetes or vascular disease are nearly five times more likely than whites to have a leg amputated and that women in Mississippi are far less likely to have mammograms than those in Maine. The study, by researchers at Dartmouth, examined Medicare claims for evidence of racial and geographic disparities and found that on a variety of quality indices, blacks typically were less likely to receive recommended care than whites within a given region. But the most striking disparities were found from place to place. For instance, the widest racial gaps in mammogram rates within a state were in California and Illinois, with a difference of 12 percentage points between the white rate and the black rate. But the country's lowest rate for blacks - 48 percent in California - was 24 percentage points below the highest rate - 72 percent in Massachusetts. The statistics were for women ages 65 to 69 who received screening in 2004 or 2005. In all but two states, black diabetics were less likely than whites to receive annual hemoglobin testing. But blacks in Colorado (66 percent) were far less likely to be screened than those in Massachusetts (88 percent). The study was commissioned by the nation's largest health-related philanthropy, the Robert Wood Johnson Foundation, which on Thursday planned to announce a three-year, $300 million initiative intended to narrow health care disparities across lines of race and geography.