title: External validity: a forgotten issue?
authors.forename: Sandro
authors.initials: S
authors.lastname: Palla
authors.forename: Mauro
authors.initials: M
authors.lastname: Farella
mesh_terms: D015982:Bias; D035061:Control Groups; D006801:Humans; D008310:Malocclusion / Q000150:complications; D018579:Patient Selection; D015203:Reproducibility of Results; D012107:Research Design; D012307:Risk Factors; D013001:Somatoform Disorders / Q000209:etiology; D013705:Temporomandibular Joint Disorders / Q000145:classification* / Q000175:diagnosis / Q000209:etiology