Table 3.

Methodological quality of cross-sectional studies

Study	Representative-ness of the sample	Sample size	Non-respondents	Ascertainment of the exposure	Comparability	Assessment of the outcome	Statistical test
Cheng, 2014	-	*	-	**	--	*	*
Cho, 2008	*	*	-	**	--	*	*
Dalbudak, 2014	*	*	-	**	--	*	*
Dalbudak, 2015	*	*	-	**	--	*	*
Hyun, 2015	-	*	*	**	--	*	*
Jelenchick, 2014	-	*	-	**	--	*	*
Ko, 2008	-	*	-	**	--	*	*
Metin, 2015	-	*	-	**	--	*	*
Sofia, 2016	-	*	-	**	--	*	*
Yen, 2007	*	*	*	**	--	*	*
Yen, 2009	*	*	-	**	--	*	*
Yen, 2016	-	*	-	**	--	*	*
Yoo, 2004	-	*	-	**	--	*	*

A study could be awarded a maximum of one star for each item except for the item Comparability