Table 3

Quality assessment of the included studies

Study	Representativeness of exposed cohort	Selection of non-exposed cohort	Ascertainment of exposure	Outcome was not present at start of study	Comparability	Assessment of outcomes	Length of follow-up	Adequacy of follow-up	Total
The Newcastle-Ottawa Quality Assessment Scale
Amarilyo et al 26	✷		✷	NA	✷	✷	✷		5/8
Dallaire et al 25	✷		✷	NA	✷	✷	✷	✷	6/8
Dhanrajani et al 30	✷		✷	NA	✷✷	✷	✷	✷	7/8
Huang et al 31	✷	✷	✷	NA		✷	✷	✷	6/8
Kim et al 27	✷		✷	NA		✷	✷	✷	5/8
Kuo et al 28	✷	✷	✷	NA		✷	✷	✷	6/8
Lee et al 29	✷		✷	NA	✷	✷	✷	✷	6/8
Melish et al 32	✷	✷	✷	NA	✷	✷			5/8
Rahbarimanesh et al 33	✷	✷	✷	NA		✷	✷	✷	6/8

>6 stars means high quality; 5–6 stars means medium quality; <5 stars means low quality.
NA, not applicable.