Table 2.

Quality assessment based on the NOS of the included studies in this meta- analysis.

References	Representativeness of the exposed cohort	Selection of the unexposed cohort	Ascertainment of exposure	Outcome of interest not present at start of study	Control for important factor or additional factor	Outcome assessment	Follow-up long enough for outcomes to occur	Adequacy of follow-up of cohort	Total quality scores
Tellini et al. (17)	⋆	⋆	⋆	⋆	⋆	⋆	⋆	⋆	8
Shum et al. (18)	⋆	⋆	⋆	⋆	⋆⋆	⋆	⋆	⋆	9
Petros et al. (19)	⋆	⋆	⋆	⋆	⋆⋆	⋆	⋆	⋆	9
Marchinena et al. (20)	⋆	⋆	⋆	⋆	⋆	⋆	⋆	⋆	8
Chen et al. (21)	⋆	⋆	⋆	⋆	⋆⋆	⋆	⋆	—	8
Bansal et al. (22)	⋆	⋆	⋆	⋆	⋆	⋆	⋆	—	8
Shah et al. (23)	⋆	⋆	⋆	⋆	⋆	⋆	⋆	⋆	8
Maurice et al. (24)	⋆	⋆	⋆	⋆	⋆⋆	⋆	⋆	⋆	9
Kang et al. (25)	⋆	⋆	⋆	⋆	⋆	⋆	⋆	⋆	8
Schiavina et al. (26)	⋆	⋆	⋆	⋆	⋆⋆	⋆	⋆	—	8
Khalifeh et al. (27)	⋆	⋆	⋆	⋆	⋆⋆	⋆	⋆	—	8
Ani et al. (28)	⋆	⋆	⋆	⋆	⋆⋆	⋆	⋆	⋆	9
Bensalah et al. (29)	⋆	⋆	⋆	⋆	⋆⋆	⋆	⋆	⋆	9

Nine stars was defined as a full score; 8–9 stars was considered as being of high methodological quality; and 0–7 stars was considered as being of poor quality.