“…However, we only investigated the working-age population. Therefore, headache [ 14 , 15 ], migraine [ 15 , 16 , 17 ], chronic daily headache (CDH) [ 14 , 15 , 17 , 18 , 19 , 20 , 21 , 22 ], and MOH [ 12 , 14 , 15 , 17 , 19 , 21 ] prevalence among the elderly in recent years was not sufficiently investigated by a population-based survey in Japan. CDH in this context means as a case with headaches occurring at least 15 days per month for three or more consecutive months [ 14 , 15 , 17 , 18 , 19 , 20 , 21 , 22 ].…”