Table 2.

Modified Newcastle–Ottawa quality assessment scale for included studies

Reference	Design	Selection (++++)	Comparability (++)	Outcome (++++)	Quality
Bauer (2008)	Case–control	++++	++	++	Good
Nunes et al. (2009)	Case–control	++	++	++++	Fair
López et al. (2014)	Cross-sectional	+++	++	++++	Good
López et al. (2016)	Cross-sectional	+++	++	++++	Good
Speer and Soldan (2015)	Case–control	+++	++	+++	Good
Sundgren et al. (2015)	Case–control	++++	++	++	Good
Moussard et al. (2016)	Case–control	+++	+	++	Fair
Amodio et al. (2017)	Cross-sectional	+++	++	+++	Good
Fleck et al. (2017)	Cross-sectional	+++	++	+++	Good
Gu et al. (2018)	Case–control	++++	++	++	Good
Martínez et al. (2018)	Cross-sectional	+++	++	++++	Good
Alonso et al. (2019)	Cross-sectional	+++	++	+++	Good
Fleck et al. (2019)	Cross-sectional	++++	++	++++	Good
Babiloni et al. (2020)	Cross-sectional	+++	++	++++	Good
Gajewski et al. (2020)	Cross-sectional	+++	++	++++	Good
Yang and Lin (2020)	Cross-sectional	+++	+	+++	Good

Note: Each (+) represents one point. Good quality: Minimum of 3(+) on selection domain, 1(+) in comparability domain, and 2(+) in outcome domain. Fair quality: Minimum of 2(+) on selection domain, 1(+) on comparability domain, and 2(+) in outcome domain. Poor quality: Minimum of 1(+) point on selection domain. Rating system based on McPheeters and colleagues (2012).