Table 6.

Assessment of study quality

Study	Quality indicators from the Newcastle-Ottawa scale									Score
	Selection				Comparability		Exposure/Outcome
	1	2	3	4	5a	5b	6	7	8
Suda Takashi [13]	Yes	Yes	No	Yes	Yes	Yes	Yes	Yes	Yes	8
Hsu C-P [12]	Yes	Yes	No	Yes	Yes	No	Yes	Yes	Yes	7
Wang, H [15]	Yes	Yes	No	Yes	Yes	Yes	Yes	Yes	Yes	8
Yano Motoki [10]	Yes	Yes	No	Yes	Yes	Yes	Yes	Yes	Yes	8
Lu Qiang [9]	Yes	Yes	No	Yes	Yes	Yes	Yes	Yes	Yes	8
Zhang Louqian [8]	Yes	Yes	No	Yes	Yes	Yes	Yes	Yes	Yes	8
Yong Tang [14]	Yes	Yes	No	Yes	Yes	No	Yes	Yes	Yes	7