Self-report Measures.— Patients provided demographic data following a standardized history. Key elements of the clinical history, including family history, headache features, temporal profile, and intake medication were assessed. In the development of this clinical prediction rule (CPR), we chose those variables most commonly seen in headache. Self-report measures included a head- neck diagram to assess the location of pain symptoms, a headache diary, the Medical Outcomes Study 36-Item Short Form (SF-36), Neck Disability Index (NDI), the Beck Depression Inventory (BDI-II) and the Headache Disability Inventory (HDI). A headache diary was used to substantiate the diagnosis. 23 On this diary, patients registered the number of days with headache (days/week), the headache duration (hours/day), and the headache intensity on an 11-cm numerical pain rate scale 24 (range 0 = no pain, 10 = maximum pain). The SF-36 is a self- administered, 36-item questionnaire assessing health-related functions in 8 domains: physical functioning; role limitations because of physical problems; body pain; vitality; general health perception; social functioning; role limitations because of emotional problems and mental health.