Excerpt: When Medicare implemented its APC-based (Ambulatory Payment Classifications) hospital outpatient prospective payment system (OPPS) four years ago, a rapid diffusion of this or similar payment systems into the commercial sector was expected. Many state Medicaid programs, Blue Cross plans, and commercial insurers had piggy-backed on Medicare's success with inpatient DRGs (diagnosis-related groups)and had achieved cost savings on inpatient services by implementing some variation of[.]