Fig. 1From: Prevalence of primary headaches in Germany: results of the German Headache Consortium StudyScreening procedure. Eighteen thousand randomly selected subjects received a questionnaire via postal mail. Subjects who did not respond were called for at least eight times for an interview by telephone. Main reasons for non-response by phone were that subjects were not available or refused the interview. Overall, we obtained information per mailed questionnaire or telephone interview from n = 9,944Back to article page