title: Epidemiology in practice: case-control studies.
authors.affiliation: BC Centre for Epidemiologic & International Ophthalmology, University of British Columbia, St Paul's Hospital, Vancouver V6Z 1Y6, Canada.
authors.forename: S
authors.initials: S
authors.lastname: Lewallen
authors.forename: P
authors.initials: P
authors.lastname: Courtright