Table 2.

Risk of bias assessment.

	Potential Risk of Bias Domain
Retrospective Studies	1	2	3	4	5	6	Risk of Bias
Iboshi et al. [41]	-	+	-	-	-	+	High
Lee et al. [42]	-	+	+	+	-	+	High
Slider et al. [43]	+	-	+	+	-	+	High
Brughelli et al. [44]	+	+	-	+	-	+	High
Mendiguchia et al. [39]	+	+	+	+	+	-	Low
Daly et al. [45]	+	+	-	+	-	+	High
Barreira et al. [46]	+	+	-	+	-	+	High
Schuermans et al. [47]	+	-	-	-	-	+	High
Haugen et al. [48]	-	+	-	+	-	+	High
Higashihara et al. [49]	+	+	-	-	-	+	High
Lord et al. [38]	+	+	+	+	-	+	Low
Crow et al. [50]	+	+	-	-	-	+	High
Ishøi et al. [40]	+	+	+	+	-	+	Low
Edouard et al. [51]	+	-	-	+	-	+	High
Prospective studies
Schuermans et al. [52]	+	-	-	+	-	+	High
Schuermans et al. [47]	+	-	-	-	-	+	High
Haugen et al. [48]	-	+	-	+	-	+	High
Kenneally-Dabrowski et al. [53]	+	+	-	+	-	+	High
Edouard et al. [51]	+	-	-	+	-	+	High

1, study participation; 2, study attrition; 3, prognostic factor measurement; 4, outcome measurement; 5, study confounding factor; 6, statistical analysis and reporting.