title: Research methods.
authors.forename: Dagmar Else
authors.initials: DE
authors.lastname: Slot
authors.forename: Theodorus Dirk
authors.initials: TD
authors.lastname: Mettes
authors.affiliation: Department of Periodontology, Academic Centre for Dentistry, Amsterdam, The Netherlands.
authors.forename: Fridus
authors.initials: F
authors.lastname: Van der Weijden
mesh_terms: D006302:Health Services Research; D006801:Humans; D012107:Research Design