title: Bias introduced by conditioning on an intermediate variable: Comment on the article by Zhang et al.
authors.forename: Yanyan
authors.initials: Y
authors.lastname: Zhu
mesh_terms: D015982:Bias; D018450:Disease Progression; D006801:Humans; D020370:Osteoarthritis, Knee / Q000000981:diagnostic imaging / Q000209:etiology*; D011859:Radiography; D016032:Randomized Controlled Trials as Topic / Q000379:methods*; D012107:Research Design; D018570:Risk Assessment; D012307:Risk Factors