Flow diagram of the enrollment process.

Abstract

We first identified 996,430 patients between 1 January 1996 and 31 December 2012 from the outpatient claim. We excluded patients who had some pre-existing diseases before the index date, had missed data, and could not match well for both cohorts. Finally, a total of 43294 patients with newly diagnosed headache other than migraine were identified as the non-migraine headache cohort. For each patient in the non-migraine headache cohort, 4 control patients were randomly selected, with frequency matching by age and sex.</p