Table 2. Quality assessments of case–control studies according to the NOS.

Study ID	Authors	Year	Selection				Comparability		Exposure			Total score
			a	b	c	d	e	f	g	h	i
1	Duraes et al. [9]	2014	*	*	/	*	*	/	*	*	*	7
2	Kutluturk et al. [11]	2013	*	*	/	*	*	/	*	*	*	7
3	Jurecka-Lubieniecka et al. [17]	2013	*	*	/	*	*	/	*	*	*	7
4	Anvari et al. [12]	2010	*	*	/	*	*	/	*	*	*	7
5	Gu et al. [13]	2010	*	*	/	*	*	*	*	*	*	8
6	Shiau et al. [14]	2007	*	*	/	*	*	/	*	*	*	7
7	Chen et al. [15]	2005	*	*	/	*	*	*	*	*	*	8
8	Bednarczuk et al. [8]	2004	*	*	/	/	*	/	*	*	*	6
9	Simmonds et al. [6]	2004	*	*	*	*	*	/	*	*	*	8
10	Kamizono et al. [16]	2000	*	*	/	*	*	/	*	*	*	7

Publication quality check list

Selection: a: Is the case definition adequate? b: Representativeness of the cases. c: Selection of controls; d: Definition of controls.

Comparability: e: Study controls for ethnicity. f: Study controls for any additional factor.

Exposure: g: Ascertainment of exposure. h: Same method of ascertainment for cases and controls. i: Non-response rate.

The asterisks (*) represent the stars in the NOS assessment.