title: Some unsolved problems in the epidemiology of headache.
authors.forename: D K
authors.initials: DK
authors.lastname: Ziegler
mesh_terms: D003430:Cross-Sectional Studies; D006261:Headache / Q000453:epidemiology* / Q000209:etiology; D006801:Humans; D015994:Incidence; D008881:Migraine Disorders / Q000453:epidemiology* / Q000209:etiology; D014481:United States / Q000453:epidemiology