title: Direction of causation models.
authors.affiliation: Veterans Administration Medical Center, Hines.
authors.forename: J
authors.initials: J
authors.lastname: Goldberg
authors.forename: V
authors.initials: V
authors.lastname: Ramakrishnan
mesh_terms: D015984:Causality; D015331:Cohort Studies; D003430:Cross-Sectional Studies; D006801:Humans; D008957:Models, Genetic; D018433:Twin Studies as Topic; D014427:Twins / Q000235:genetics*