Table 3. The NOS quality assessment of the included studies.

Study ID	Selection			Comparability			Outcome		Total
	Representativeness of the exposed cohort	Selection of the non-exposed cohort	Ascertainment of exposure	Demonstration that outcome of interest was not present at the start of the study	Comparability of cohorts on the basis of the design or analysis	Assessment of outcome	Was follow-up long enough for outcomes to occur	Adequacy of follow-up of cohorts
Caras et al. (2017)	★	★	★	★	★☆	☆	★	★	7
Chan et al. (2013)	☆	★	★	★	★☆	★	★	☆	6
Cho et al. (2014)	★	★	★	★	★☆	★	★	☆	7
Cui et al. (2017)	★	★	★	★	★☆	★	★	☆	7
Djaladat et al. (2014)	★	★	☆	★	★☆	★	★	★	7
Fujita et al. (2015)	★	★	☆	★	★☆	★	★	☆	6
Garg et al. (2014)	★	★	☆	★	★☆	★	★	★	7
Hinata et al. (2015)	★	☆	★	★	★☆	★	★	★	7
Huang et al. (2017)	☆	★	★	★	★☆	★	★	★	7
Johnson et al. (2015)	★	☆	★	★	★☆	★	★	★	7
Kluth et al. (2014)	★	★	★	★	★☆	★	★	☆	7
Krane et al. (2013)	☆	☆	★	★	★☆	★	★	★	6
Ku et al. (2015)	★	★	★	★	★☆	★	★	☆	7
Lambert et al. (2013)	☆	★	★	★	★☆	★	★	★	7
Laurent et al. (2017)	★	★	★	★	★☆	★	☆	★	7
Lavallee et al. (2014)	★	★	☆	★	★☆	★	★	★	7
Liu et al. (2016)	☆	★	★	★	★☆	★	☆	★	6
Morgan et al. (2011)	☆	★	★	★	★☆	★	★	★	7
Mursi et al. (2013)	☆	★	☆	★	★☆	★	☆	★	5
Nakagawa et al. (2017)	★	★	★	★	★☆	★	★	☆	7
Sharma et al. (2016)	☆	★	☆	★	★☆	★	★	★	6
Sheth et al. (2016)	☆	★	★	★	★☆	★	★	★	7
Taguchi et al. (2016)	★	★	☆	★	★☆	★	★	★	7

★ indicates that a score (1) was assigned; ☆ indicates a score of zero.