“…Of the 25 studies, 21 were prospective [ 10 , 21 , 22 , 29 , 36 - 52 ], 1 was retrospective [ 53 ], and the remaining 3 studies did not report the study design [ 23 , 54 , 55 ]. In all, 20 studies used PTA as the index test [ 10 , 21 , 22 , 29 , 36 - 42 , 44 - 46 , 48 - 52 , 54 ], whereas the remaining 5 studies applied a speech recognition test (SRT) as the index test [ 23 , 43 , 47 , 53 , 55 ]. A total of 4 studies enrolled elderly participants [ 10 , 36 , 37 , 39 ], whereas 7 studies included children [ 21 - 23 , 38 , 41 , 49 , 55 ], and 13 studies enrolled adult participants [ 29 , 40 , 42 - 44 , 46 , 48 - 54 ].…”