Fig. 1From: Headache following head injury: a population-based longitudinal cohort study (HUNT)Flow of participants through the HUNT2 and HUNT3 study and selection of head injury patients. aComplete non-participants: Answering no questionnaire. Partial non-participants: Answering part of the questinonnaire, but not the headache screening question. Abbreviations: HUNT = the Nord-Trøndelag Health StudyBack to article page