“…Of the 29 studies, 15 assessed prevalence or relative frequency of premonitory symptoms as the primary outcome [ 17 , 19 , 21 – 25 , 28 , 31 – 33 , 35 , 37 – 39 ]. Nine of the 22 clinic-based studies collected data prospectively [ 17 , 18 , 22 , 23 , 26 , 27 , 35 , 36 , 39 ], while 14 [ 19 – 21 , 24 , 25 , 28 , 30 – 34 , 37 , 38 , 40 ], and all six population-based studies [ 13 – 16 , 41 , 42 ], acquired data retrospectively.…”