“…24,25,33,36,38,45,47 In contrast, 15 studies used specific control groups. [26][27][28][29][30][31]37,40,46,[48][49][50][51][52][53] A total of seven studies compared various subgroups within the sample population. 32,34,35,[41][42][43][44] (Tables 3 and 4) (see Appendix, Supplemental Digital Content 1, for content analysis, http://links.lww.com/PRS/ B188).…”