Fig. 1

Disposition of subjects during the study. 1 The study base: respondents who provided data in 2005, 2006, 2007 and EM in either 2005 or 2006 or both. 2 1,921 participants with EM in 2006 but not 2005. 3 Of the 6,360 controls in 2006, 5,312 meet ICHD-2 criteria for EM and 1,048 has other outcomes including PM and ETTH. 4 137 subjects with other outcomes were excluded because they developed CM in 2008. 5 The EM subjects in 2006 included 5,331 with EM in 2005 and 2006, and 1,921 subjects with EM in 2006 but not 2005 for a total of 6,852. 6 The 6,708 control subjects in 2007 included 5,212 with EM, 759 with PM, 691 with ETTH and any other outcomes. EM episodic migraine, CM chronic migraine