Independence Blue Cross, the Philadelphia region’s largest health insurer, said Monday its accountable-care organization payment model is yielding tangible results. According to IBC, about 90 percent of region’s health care delivery systems are participating in the ACO payment model. Accountable Care Organizations are typically groups of doctors, hospitals, and other health-care providers that work together to provide coordinated quality care to patients. The IBC accountable care payment model requires health-care providers, typically a hospital and its affiliated primary-care doctors and specialists, to establish an ACO-like entity that shares responsibility with the insurer for improving clinical performance and cost efficiency for the care delivered to patients.