Study population and survey process

The data of the Korean Headache-Sleep Study (KHSS) were used in the present study. The KHSS was a nation-wide, cross-sectional survey regarding headache and sleep disorder among Korean adults aged 19 to 69 years. It also included items regarding symptoms of anxiety and depression. The study design, methods, and process were described in detail previously [6]. In brief, the KHSS adopted a two-stage clustered random sampling method for all Korean territories except Jeju-do. This method sampled participants proportionally to the population distribution and socioeconomic status. Trained interviewers conducted the survey by face-to-face interviews using a questionnaire. All trained interviewers were employees of Gallup Korea and had previous experience in social surveys. Data collection of the KHSS was performed from November 2011 to January 2012. The KHSS was approved by the Institutional Review Board and Ethics Committee of Hallym University Sacred Heart Hospital (IRB No. 2011-I077). Written informed consent was obtained from all participants.