Table 2.

Modified Newcastle-Ottawa quality assessment scale for cohort studies included in the meta-analysis

Ref.	Selection				Comparability1	Outcome			Overall
	Representativeness	Selection	Ascertainment	Incident disease		Assessment	Length of follow-up	Adequacy of follow-up	Quality Score (Maximum 9)
Song et al[28]	↓	↓	↓	↑	↑	↓	↓	↓	6
Kim et al[29]	↓	↓	↓	↑	↓↓	↓	↓	↓	8
Kim et al[30]	↓	↓	↓	↑	↓↓	↓	↓	↓	8
Ikegami et al[31]	↓	↓	↓	↑	↑	↓	↓	↓	6
Lee et al[32]	↓	↓	↓	↑	↑	↓	↓	↓	6
Shen et al[33]	↓	↓	↓	↑	↑	↓	↓	↓	6
Heffron et al[34]	↓	↓	↓	↑	↑	↓	↓	↓	6
Stewart et al[35]	↓	↓	↓	↑	↓↓	↓	↓	↓	8
Iwamoto et al[36]	↓	↓	↓	↑	↑	↓	↓	↓	6
Toso et al[20]	↓	↓	↓	↑	↑	↓	↓	↓	6
Saito et al[37]	↓	↓	↓	↑	↑	↓	↓	↓	6
Koukoutsis et al[19]	↓	↓	↓	↑	↑	↓	↓	↓	6
Ueda et al[18]	↓	↓	↓	↑	↑	↓	↓	↓	6
Heffron et al[38]	↓	↓	↓	↑	↑	↓	↓	↓	6
Bjøro et al[17]	↓	↓	↓	↑	↑	↓	↓	↓	6
Chui et al[39]	↓	↓	↓	↑	↑	↓	↓	↓	6
Cacciarelli et al[16]	↓	↓	↓	↑	↑	↓	↓	↓	6
Lo et al[40]	↓	↓	↓	↑	↑	↓	↓	↓	6
Sanchez et al[41]	↓	↓	↓	↑	↓↓	↓	↓	↓	8
Reding et al[15]	↓	↓	↓	↑	↑	↓	↓	↓	6
Gugenheim et al[5]	↓	↓	↓	↑	↑	↓	↓	↓	6

¹A maximum of two downward arrows (↓↓) can be given for comparability. ↓ : Consistent with criteria and low risk of bias; ↑ : Not consistent with criteria and high risk of bias.