Table 3.

Quality assessment of case control studies using New Castle Ottawa Scale

First author	Selection				Comparability		Exposure
	Case definition is adequate	Consecutive or obviously representative series of cases	Community controls	No history of disease (endpoint) in controls	Study controls for the most important factor	Study controls for any additional factor	Secure record/structured interview blind to case/control status	Same method for ascertainment for cases and controls	Nonresponse rate same for both groups
Hiraki, 2008[22]	-	*	-	*	*	*	-	*	-
Mai, 2014[26]	*	*	-	-	-	*	-	*	-
Chrysanthakopoulos, 2016[28]	*	*	*	*	*	*	*	*	-
Yoon, 2019[32]	-	*	*	*	-	*	-	-	*

*Significant and -nonsignificant