Guyatt ' s responsiveness index was 0 . 54 for the SF - 8 , 0 . 61 for the Jackson , 0 . 71 for the WURSS - 44 , and 0 . 80 for the WURSS - 21 , suggesting that a two - armed trial would require 74 participants for the WURSS - 21 , 92 for the WURSS - 44 , 124 for