President Obama has signed the so-called “doc fix” law to overhaul how doctors receive payment under Medicare, the federal health insurance program for seniors and people with disabilities. The bill averts a cut in doctors’ pay, embracing a structure aimed at rewarding doctors for quality of care, rather than the number of office visits. It also extends a children’s healthcare program for another two years. But the measure cuts billions of dollars from Medicare and increases insurance costs for higher-income seniors. The group Physicians for a National Health Program has criticized the measure as a step toward Republicans’ goal of privatizing Medicare.