title: Author's response: the design of observational studies-defining baseline time.
authors.affiliation: Institute for Clinical Evaluative Sciences, Toronto, Ontario, Canada. peter.austin@ices.on.ca
authors.forename: Peter C
authors.initials: PC
authors.lastname: Austin
authors.forename: Robert W
authors.initials: RW
authors.lastname: Platt
mesh_terms: D035843:Biomedical Research / Q000379:methods*; D004812:Epidemiologic Methods; D006801:Humans; D016032:Randomized Controlled Trials as Topic / Q000379:methods; D012107:Research Design; D015983:Selection Bias