Researchers long ago established that certain medical procedures are performed at dramatically different rates from place to place, and that these disparities affect the quality and cost of health care. Now, health insurers, hospitals and government agencies from the Bay Area to Washington, D.C., are getting more aggressive about tackling variation in medical care. The issue will surface in San Francisco with a collaboration that started this summer among Blue Shield of California and some local hospitals and physicians, aimed at better coordination of patient care for about 26,000 public employees. The partnership is modeled after a similar one in the Sacramento region whose early efforts to rein in variation resulted in training doctors in newer medical techniques and offering patients less-invasive treatment options. In the case of weight-loss surgeries, procedures fell in one year by 13%. Also this summer, the Centers for Medicare & Medicaid Services started using a new data-mining technology to detect and prevent fraud in the Medicare program, the federal health insurance program for people 65 and older. Extreme variation in care is one pattern the technology will be looking for.