Figure 2. Risk of bias of included studies.

Risk of bias was low (green) in six studies, ^{6 , 29 , 30 , 32 , 36 , 40} unclear (yellow) in five studies, ^{28 , 35 , 37 – 39} and high (red) in five studies. ^{27 , 31 , 33 , 34 , 41}