title: Persistent postoperative pain and the problem of strictly observational research.
authors.affiliation: Department of Anesthesiology, Centro Hospitalar São João, Oporto, Portugal.
authors.forename: Luís
authors.initials: L
authors.lastname: Guimarães-Pereira
mesh_terms: D006801:Humans; D010147:Pain Measurement; D010149:Postoperative Pain