Table 2.

Risk of bias of the studies included

Study	Randomisation process	Allocation concealment	Blinding	Incomplete outcome data addressed
Clavert et al. [4]	Low	Low	Low	High
Digas et al. [5]a	Unclear	Unclear	Unclear	Low
Digas et al. [5]a	Unclear	Unclear	Unclear	High
Engh et al. [7]	Unclear	Unclear	Low	High
Garcia-Rey et al. [8]	Unclear	Unclear	Low	Low
Glyn-Jones et al. [9]	Low	Low	Low	Low
Martell et al. [15]	Unclear	Low	Low	High
Triclot et al. [23]	Low	Low	Low	High

“High” indicates high risk of bias in the according stage; “Low” indicates low risk of bias in the according stage; “Unclear” indicates either lack of information or uncertainty over the potential for bias

^aData from two studies reported in one article