Measuring PPO performance is an inexact science at best.
The American Accreditation HealthCare Commission has found some PPOs, that are making headway in what is a fragmented and difficult task.
D000068:Accreditation / Q000458:organization & administration*; D017598:Efficiency, Organizational / Q000592:standards*; D006801:Humans; D017063:Outcome Assessment, Health Care; D011243:Preferred Provider Organizations / Q000592:standards*; D014481:United States