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; D016022:Case-Control Studies; D015986:Confounding Factors, Epidemiologic; D018865:Dental Research / Q000706:statistics & numerical data*; D006801:Humans; D015203:Reproducibility of Results; D012107:Research Design / Q000706:statistics & numerical data*; D012307:Risk Factors; D013705:Temporomandibular Joint Disorders / Q000209:etiology