Table 3.

The quality and risk of bias assessment of the included studies according to Newcastle‐Ottawa Scale for case‐control studies31

First author, year, reference number	Selection				Comparability	Exposure			NOS summarized score
	Item 1	Item 2	Item 3	Item 4	Item 5	Item 6	Item 7	Item 8
Bianchi Porro et al. (1983)35	0	*	*	*	**	*	*	0	7/9
Gwee et al. (1996)36	0	*	0	0	*	*	*	0	4/9
Vesa et al. (1998)37	*	0	*	*	*	*	*	0	6/9
Goldstein et al. (2000)38	*	*	0	0	**	*	*	0	6/9
Vernia et al. (2001)27	*	*	*	*	0	*	*	0	6/9
Parry et al. (2002)39	*	*	0	*	*	*	*	0	6/9
Lanng et al. (2003)40	*	*	*	*	**	*	*	0	8/9
Farup et al. (2004)41	*	*	*	*	**	*	*	0	8/9
Saberi‐Firoozi et al. (2007)42	*	*	*	0	0	*	0	0	4/9
Corlew‐Roath et al. (2009)43	*	*	0	0	0	*	*	0	4/9
Yakoob et al. (2011)44	*	*	0	*	**	*	*	*	8/9
Kumar et al. (2012)45	*	*	0	0	**	*	*	0	6/9
Yang et al. (2013)26	*	*	0	*	**	*	*	0	7/9
Xiong et al. (2017)46	*	*	*	*	**	*	*	*	9/9

The NOS consists of eight numbered items, divided into three main sections (selection, comparability, and exposure). Each numbered item can be rewarded with maximum one star; comparability can be awarded with two stars. The studies with maximum of nine stars representing the highest‐quality trials with the lowest risk of bias. The detailed analysis of each study is represented in Table S3.

NOS, Newcastle‐Ottawa Scale.