Table 2. Risk of bias assessment.

Variable	Study
	Danquah I, et al. 19	Wyss K, et al. 18	Khuu D, et al. 17
Bias due to confounding	Serious risk of bias	Serious risk of bias	Serious risk of bias
Bias in selection of participants into the study	Critical risk of bias	Low risk of bias	Critical risk of bias
Bias in classification of interventions	Low risk of bias	Low risk of bias	Low risk of bias
Bias due to missing data	No information	No information	No information
Bias in measurement of outcomes	Moderate risk of bias	Moderate risk of bias	Moderate risk of bias
Bias in selection of the reported result	Moderate risk of bias	Moderate risk of bias	Moderate risk of bias
Judgement	Critical risk of bias	Critical risk of bias	Critical risk of bias