Table 2.

Newcastle–Ottawa Scale scores of included studies.

	Selection				Comparability	Outcome
Study	Representativeness of the exposed cohort	Selection of the nonexposed cohort	Ascertainment of exposure	Demonstration that outcome of interest was not present at start of 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	Total scores
Ezoe 2011	★	★	★	★	★	★	★		7
Hashimoto 2011	★	★	★	★	★★	★	★		8
Yamaguchi 2011	★	★	★	★	★		★	★	7
Hanaoka 2012	★	★	★	★	★★	★	★	★	9
Kataoka 2014	★	★	★	★	★	★	★	★	8
Nagami 2015		★	★	★	★★			★	6
Kadota 2016	★		★	★	★	★	★	★	7
Tsujii 2017	★	★	★	★	★★	★	★	★	9
Zhou 2017	★		★	★	★★	★	★	★	8
Iizuka 2017			★	★	★★	★		★	6
Pih 2019	★	★	★	★	★★		★	★	8
Chu 2019			★	★	★★	★	★	★	7
Yang 2019	★		★	★	★★		★		6
Nie 2019	★	★	★	★	★★	★	★	★	9
Hashimoto 2019	★	★	★	★	★★	★	★		8
Sakaguchi 2020	★		★	★	★	★	★		6
Zhou 2021		★	★	★	★★	★	★	★	8