The prevalence of narrow physician networks in the Health Insurance Marketplaces varied widely by state in 2014, according to a new study by researchers at the University of Pennsylvania’s Leonard Davis Institute of Health Economics. The study considers networks narrow if 25% or fewer physicians in a rating area participate. Twelve states had no narrow networks, while the prevalence in other states ranged from 83% in Georgia to 13% in Idaho and North Carolina. States with a high prevalence of narrow networks (60% or more) were dominated by Health Maintenance Organizations, while states with the lowest prevalence (20% or less) were dominated by Preferred Provider Organizations, the study found.