Table 2.

Results of risk of bias assessment.

Study	Random sequence generation	Allocation concealment	Blinding of participants and personnel	Blinding of outcome assessment	Incomplete outcome data	Selective reporting	Other bias	Overall study quality
Calear et al [42]	+a	+	?b	?	+	?	+	Poor
Fleming et al [43]	+	+	+	+	+	+	?	Good
Ip et al [44]	+	+	+	+	+	?	+	Good
Merry et al [45]	+	+	+	+	−c	+	+	Fair
Poppelaars et al [46]	+	?	+	+	+	?	+	Poor
Sekizaki et al [47]	−	?	−	−	+	?	+	Poor
Smith et al [48]	+	?	?	?	+	?	+	Poor
Spence et al [39]	+	?	+	+	+	?	+	Fair
Sportel et al [49]	+	+	+	+	+	+	+	Good
Stallard et al [50]	?	+	?	?	+	?	+	Poor
Stasiak et al [51]	+	+	+	+	+	?	+	Good
Stjerneklar et al [40]	+	+	+	+	+	?	+	Good
Topooco et al [52]	+	+	+	−	+	?	+	Poor
Wong et al [53]	?	?	?	?	−	?	+	Poor
Wright et al [54]	+	?	?	?	+	?	+	Poor
Wuthrich et al [41]	+	?	?	?	+	?	−	Poor

^a+: low risk of bias.

^b?: unclear risk of bias.

^c−: high risk of bias.