Wintzer-Wehekind J, Horlick E, Ibrahim R, Cheema AN, Labinaz M, Nadeem N, Osten M, Cote M, Marsal JR, Rivest D, Marrero A, Houde C, Rodes-Cabau J. Effect of clopidogrel and aspirin vs aspirin alone on migraine headaches after transcatheter atrial septal defect closure: one-year results of the CANOA randomized clinical trial. JAMA Cardiol. 2021 Feb 1;6(2):209-13. doi: 10.1001/jamacardio.2020.4297
Drummond FJ, Sharp L, Carsin AE, Kelleher T, Comber H. Questionnaire order significantly increased response to a postal survey sent to primary care physicians. J Clin Epidemiol. 2008 Feb;61(2):177-85. doi: 10.1016/j.jclinepi.2007.04.012