Table 4.

Risk of bias assessment.

	Study participation	Study attrition	Prognostic factor measurement	Outcome measurement	Study confounding	Statistical analysis and reporting	Overall risk of bias	Included in quantitative synthesis
Yang et al. (27)		n.a.						yes
Osterlind et al. (28)		n.a.						no
Zarzecka et al. (29)		n.a.						no
Hermes et al. (30)		n.a.						no
Wang et al. (31)		n.a.						no
Berardi et al. (32)		n.a.						yes
Sengupta et al. (33)		n.a.						no
Kobayashi et al. (34)		n.a.						no
Fucá et al. (35)								yes
Alamoudi (36)								no
Hansen et al. (37)		n.a.						yes
Svaton et al. (38)		n.a.						yes
Allan et al. (39)		n.a.						no
Li et al. (40)		n.a.						no
Osterlind et al. (41)		n.a.						no
Doshi et al. (42)		n.a.						no
Johnson et al. (43)								no
Jacot et al. (45)		n.a.						no
Umemura et al. (51)		n.a.						no
Sagman et al. (44)		n.a.						no
Hong et al. (46)		n.a.						yes
Maestu et al. (47)		n.a.						no
Kawahara et al. (48)		n.a.						no
Cerny et al. (49)		n.a.						yes
Ma et al. (50)		n.a.						yes
Jacot et al. (52)		n.a.						no
Rechnitzer et al. (53)		n.a.						no
Bose et al. (54)		n.a.						no
Rinaldi et al. (55)		n.a.						no
Chan et al. (56)		n.a.						no
Huang et al. (57)		n.a.						no
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