“…In total 50 (90.0%) of the 55 studies included a subjective assessment, 21 (42.0%) of which used qualitative methods [25, 28, 32, 33, 36, 39, 40, 42, 45, 47, 50, 52–54, 57, 63, 66, 67, 69, 73, 75] and 38 (76.0%) of which used quantitative methods [26, 27, 29–32, 34, 35, 37–42, 45, 48, 49, 51, 52, 55–57, 59–62, 64–66, 68, 70–72, 74, 75, 77, 78, 84]. …”