Table 2.

A quality assessment of the eligible studies based on the Newcastle–Ottawa Scale [14,15].

Study	Selection	Comparability	Outcome/Exposure	Total Score
Kasukawa et al., 2020 [16]	★★★★		★★	6
Sasaki et al., 2013 [17]	★★★★	★★	★★	8
Iizuka et al., 2015 [18]	★★★★	★★	★★	8
Taniguchi et al., 2021 [19]	★★★★		★★	6
Muramoto et al., 2012 [20]	★★★★	★★	★★	8
Muramoto et al., 2013 [21]	★★★	★★	★★	7
Muramoto et al., 2014 [22]	★★	★★	★★	6
Muramoto et al., 2016 [23]	★★	★★	★★	6
Matsumoto et al., 2016 [24]	★★★★		★★	6
Fujita et al., 2019 [25]	★★★★★	★★	★★	9
Imagama 2017 [26]	★★★★		★★★	7
Nishimura 2020 [27]	★★★		★★	5
Chiba et al., 2016 [28]	★★★	★★	★★	7
Machino et al., 2020 [29]	★★★★		★★★	7
Machino et al., 2020 [30]	★★★★★		★★★	8
Hirano et al., 2013 [31]	★★★★		★★★	7
Hirano et al., 2012 [32]	★★★★	★★	★★★	9
Hirano et al., 2013 [33]	★★★	★★	★★★	8
Hirano et al., 2012 [34]	★★★	★★	★★★	8
Ohba et al., 2021 [35]	★★★★	★★	★★★	9
Shigematsu et al., 2019 [36]	★★★	★★	★★	7
Araki et al., 2021 [37]	★★★		★★	5
Fujita et al., 2019 [38]	★★★★		★★★	7
Shimizu et al., 2021 [39]	★★★★	★★	★★	8
Kato et al., 2020 [40]	★★★★	★★	★★	8
Fujita et al., 2020 [41]	★★★★	★★	★★	8

Newcastle-Ottawa Scale for case-control studies: Selection (Maximum ★★★★)—(1) Is the case definition adequate? (2) Representativeness of the cases; (3) Selection of controls; (4) Definition of Controls. Comparability (Maximum ★★) 2013 (1) Confounding factors controlled. Exposure (Maximum ★★★)—(1) Ascertainment of exposure; (2) Same method of ascertainment for cases and controls; (3) Non-Response rate. Newcastle-Ottawa Scale for cohort studies: Selection (Maximum ★★★★)—(1) Representativeness of the exposed cohort; (2) Selection of the non-exposed cohort; (3) Ascertainment of exposure; (4) Demonstration that outcome of interest was not present at start of study. Comparability (Maximum ★★)—(1) Confounding factors controlled. Outcome (Maximum ★★★)—(1) Assessment of outcome; (2) Was follow-up long enough for outcomes to occur; (3) Adequacy of follow up of cohorts. Newcastle-Ottawa Scale adapted for cross-sectional studies: Selection (Maximum ★★★★★)—(1) Representativeness of the sample; (2) Sample size; (3) Non-respondents; (4) Ascertainment of the exposure. Comparability: (Maximum ★★)—(1) Confounding factors controlled. Outcome (Maximum ★★★)—(1) Assessment of outcome; (2) Statistical test.