Table 4.

The Newcastle‐Ottawa Scale for all studies that included in the quantitative synthesis.

Study	Sample size, n	Selection	Comparability	Outcome	Total
Wang et al. (2020) [16]	236	****	**	**	8
Jaidane et al. (2010) [5]	170	****	**	**	8
Ham et al. (2009) [3]	203	***	**	**	7
Park et al. (2009) [17]	189	****	**	**	8
Ugurlu et al. (2007) [12]	65	****	*	**	7
Tsivian et al. (2003)* [4]	51	***	*	**	6
Vicente et al. (1988) [13]	200	***	*	**	6
Laor et al. (1981) [14]	287	**	**	**	6
Greene et al. (1972) [15]	200	***	*	**	6

Each asterisk (*) represents an individual criterion within the subsection that was fulfilled.

[Correction added on 14 August 2020, after first online publication: A reference has been amended in this version.]