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2. Silberstein SD, Lipton RB: Chronic daily headache, including transformed migraine, chronic tension-type headache, and medication overuse. In Wolffs Headache and Other Head Pain. Oxford: Oxford University Press; 2001:247–282.
3. Castillo J, Munoz P, Guitera V, Pascual J: Epidemiology of chronic daily headache in the general population. Headache 1999, 38:497–506.
4. Bigal ME, Sheftell FD, Rapoport AM, et al.: Chronic daily headache in a tertiary care population: correlation between the international headache society diagnostic criteria and proposed revisions of criteria for chronic daily headache. Cephalalgia 2002, 22:432–438.
5. Koenig MA, Gladstein J, McCarter RJ, et al. and the pediatric committee of the American Headache Society: Chronic daily headache in children and adolescents presenting to tertiary headache clinics. Headache 2002, 42:491–500.