Congress created private Medicare Advantage health plans 11 years ago to help control health care spending on the elderly. But a Center for Public Integrity investigation found that billions of tax dollars are wasted every year through manipulation of a Medicare payment tool called a “risk score.” The formula is supposed to pay health plans more for sicker patients and less for healthy people, but often it pays too much. The government has for years missed opportunities to corral tens of billions of dollars in overcharges and other billing errors tied to abuse of risk scores. Meanwhile, the growing power of the Medicare Advantage industry has muzzled many critics in Congress, and turned others into cheerleaders for the program.