Table 2. Quality assessment according to the Newcastle–Ottawa scale of the included studies.

Author	Selection	Comparability	Exposure	Total score
Park et al[38]	2	2	3	8
Subramaniam et al[39]	2	2	3	8
Subramaniam et al[10]	2	2	3	8
Lau et al[15]	2	2	3	8
Du et al[40]	2	1	3	7
Suzuki et al[11]	2	1	3	7
Li et al[41]	2	2	3	8
Qiao et al[42]	2	1	3	7
Tian et al[43]	2	1	3	7
Jiang et al[16]	2	1	3	7