Table 2.

Qualitative assessment of risk of bias using Newcastle-Ottawa Scale

Study name	Selection	Comparability	Outcome
Guo et al. (2020)	**		***
Holtmann et al. (2020)	***	*	**
Kayaaslan et al. (2020)	**		***
Li, Jin, et al. (2020)	*		**
Li, Xiao, et al. (2020)	***	*	***
Ma et al. (2020)	**		***
Pan et al. (2020)	**		***
Pavone et al. (2020)	**		***
Rawlings et al. (2020)	**		***
Ruan et al. (2020)	***	*	***
Song et al. (2020)	**		***
Temiz et al. (2020)	***	**	***
Machado et al. (2021)	**		***
Burke et al. (2021)	**		***

A total number of stars that could have been given for each domain was as follows: for “selection” four stars, for “comparability” two stars, and for “outcome” three stars