Table 3.

Results from the Newcastle-Ottawa quality assessment.

	Selection				Comparison	Outcome
Authors (year)	Representativeness (Max:⋆)	Sample size (Max:⋆)	Non-respondents (Max:⋆)	Ascertainment of the exposure (Max:⋆⋆)	Comparable outcome groups/Controlled for confounding factors (Max:⋆⋆)	Assessment of outcome (Max:⋆⋆)	Statistical test (Max:⋆)	Total
Bolat et al. (2021)	–	–	–	**	–	*	–	3*
Jeong et al. (2018)	*	–	*	**	–	*	–	5*
Khalil et al. (2020)	*	–	–	**	–	*	–	4*
Kim et al. (2017)	–	*	*	**	–	*	*	6*
Lee & Ham (2018)	*	–	–	**	**	*	–	6*
Merelle et al. (2017)	*	*	*	*	**	*	*	8*
Rehbein et al. (2010)	*	*	–	*	–	*	–	4*
Severo et al. (2020)	*	–	*	**	–	*	*	6*
Soares et al. (2020)	*	*	–	*	**	*	*	7*
Strittmatter et al. (2015)	*	*	–	**	–	*	*	6*
Wenzel et al. (2009)	*	*	*	*	**	*	–	7*
Yu et al. (2020)	*	*	–	*	**	*	*	7*