Table 2. The NOS quality evaluation.

Each asterisk (*) represents a score in the Newcastle-Ottawa Scale (NOS), a tool used to assess the quality of non-randomized controlled studies. High, NOS score > 7 points; low, NOS score < 6 points; moderate, 6–7 points.

Study	Definition adequate	Represen- tativeness of the cases	Definition of Controls	Comparability of cases and controls on the basis of the design or analysis	Ascertainment of exposure	Same method of ascertainment for cases and controls	Non response	Total scores
Atchade et al. (2020)	*	*	*	**	*	*	*	8
Balci et al. (2017)	*	*	*	**	*	*	*	8
Chan et al. (2023)	*	*	*	**	*	*	*	8
Du et al. (2021)	*	*	*	**	*	*	*	8
Fidalgo et al. (2014)	*	*	*	**	*	*	*	8
Greite et al. (2022)	*	*	*	**	*	*	*	8
Ishikawa, Griesdale & Lohser (2014)	*	*	*	**	*	*	*	8
Jacques et al. (2012)	*	*	*	**	*	*	*	8
Jing et al. (2021)	*	*	*	**	*	*	*	8
Kim et al. (2021)	*	*	*	**	*	*	*	8
Liu et al. (2021)	*	*	*	**	*	*	*	8
Lu et al. (2023)	*	*	*	*	*	*	*	7
Rocha et al. (2005)	*	*	*	*	*	*	*	7
Sikma et al. (2017)	*	*	*	**	*	*	*	8
Sang et al. (2021)	*	*	*	**	*	*	*	8
Scaravilli et al. (2022)	*	*	*	*	*	*	*	7
Toyoda et al. (2023)	*	*	*	**	*	*	*	8
Xue et al. (2014)	*	*	*	**	*	*	*	8
Zhang Shuai & Jingqing (2020)	*	*	*	*	*	*	*	7