Table 2.

Quality assessment of all included studies.

Reference	Selection Bias	Study Design	Confounders	Data Collection Method	Withdrawals	Global
[34]	1	1	3	3	3	Weak
[4]	1	1	3	3	3	Weak
[35]	1	1	3	3	3	Weak
[36]	2	1	3	3	3	Moderate
[46]	1	2	3	3	3	Moderate
[10]	1	1	3	3	3	Weak
[48]	1	2	3	3	3	Moderate
[45]	1	2	3	3	3	Moderate
[17]	1	1	3	3	3	Weak
[21]	1	1	3	3	3	Weak
[37]	1	1	3	3	3	Weak
[38]	1	1	3	3	3	Weak
[52]	3	2	3	3	3	Strong
[39]	1	1	3	3	3	Weak
[9]	2	1	3	3	3	Moderate
[40]	1	3	3	3	3	Moderate
[41]	1	2	3	3	3	Moderate
[6]	1	3	3	3	3	Moderate
[2]	1	3	3	3	3	Moderate
[49]	3	2	3	3	3	Strong
[42]	1	3	3	3	3	Moderate
[51]	2	2	3	3	3	Strong
[43]	1	3	3	3	3	Moderate
[44]	2	2	3	3	3	Moderate
[11]	1	1	3	3	3	Weak
[50]	1	1	3	3	3	Weak
[24]	2	3	3	3	3	Strong
[47]	1	2	3	3	3	Moderate

Note. 1, weak; 2, moderate; 3, strong.