title: Reply.
authors.affiliation: Department of Venous Surgery, Maastricht University Medical Centre, Maastricht, The Netherlands.
authors.forename: Fabio S
authors.initials: FS
authors.lastname: Catarinella
authors.affiliation: Department of Clinical Epidemiology and Medical Technology Assessment, Maastricht University Medical Centre, Maastricht, The Netherlands.
authors.forename: Fred H M
authors.initials: FHM
authors.lastname: Nieman
authors.affiliation: Department of Venous Surgery, Maastricht University Medical Centre, Maastricht, The Netherlands; Department of Vascular Surgery, Universitäts Klinikum, Aachen, Germany.
authors.forename: Cees H A
authors.initials: CHA
authors.lastname: Wittens