title: Headache disorders are third cause of disability worldwide.
authors.affiliation: Department of Neuroscience, Norwegian University of Science and Technology, Edvard Griegs Gate, Trondheim, Norway, t.steiner@imperial.ac.uk.
authors.forename: Timothy J
authors.initials: TJ
authors.lastname: Steiner
authors.forename: Gretchen L
authors.initials: GL
authors.lastname: Birbeck
authors.forename: Rigmor H
authors.initials: RH
authors.lastname: Jensen
authors.forename: Zaza
authors.initials: Z
authors.lastname: Katsarava
authors.forename: Lars J
authors.initials: LJ
authors.lastname: Stovner
authors.forename: Paolo
authors.initials: P
authors.lastname: Martelletti