Table 3.

Quality assessment of included studies.

RCTs	1	2	3	4	5	The overall risk of bias
Dong et al. (22)	**	**	*	*	**	**
Harber et al. (24)	**	**	*	*	**	**
Neunhäuserer et al. (23)	**	**	*	*	*	**
Non-RCTs	1	2	3	4	5	6	7	8	9
Just et al. (25)	***	**	**	*	*	*	**	*	**
Kyung et al. (15)	***	**	*	*	**	*	**	*	**
Samannan et al. (26)	***	**	*	*	**	*	*	*	**

1. Randomization process; 2. Deviation from intended intervention; 3. Missing outcome data; 4. Measurement of outcome; 5. Selection of reported results. ^*, Low risk; ^**, Some concerns; ^***, High risk.

1. Random sequence generation; 2. Allocation concealment; 3. Baseline outcome measurements similar; 4. Baseline characteristics similar; 5. Incomplete outcome data; 6. Knowledge of the allocated interventions adequately prevented during the study; 7. Protection against contamination; 8. Selective outcome reporting; 9. Other risks of bias.

^*, Low risk; ^**, Unclear; ^***, High risk.