title: PPPs--twenty years and counting.
authors.forename: Alfred
authors.initials: A
authors.lastname: Sommer
authors.forename: Richard L
authors.initials: RL
authors.lastname: Abbott
authors.forename: Flora
authors.initials: F
authors.lastname: Lum
authors.forename: H Dunbar
authors.initials: HD
authors.lastname: Hoskins
mesh_terms: D006801:Humans; D009885:Ophthalmology / Q000592:standards* / Q000639:trends; D010818:Practice Patterns, Physicians' / Q000592:standards* / Q000639:trends; D011787:Quality of Health Care