Table 2.

Newcastle–Ottawa scale for included studies

Study	Representativeness of expose of cohort	Selection of the non-exposed cohort	Ascertainment of exposure	Demonstration that outcome of interest was not present at start of study	Comparability	Assessment of outcome	Adequate follow-up length	Adequacy of followup	Score
Gondolesi GE (2004) USA	*	*	*	*	**	*	*	*	9
Roayaie S (2004) USA	*	*	*	*		*	*	*	7
Hwang S (2005) Korea	*	*	*	*	**	*	*	*	9
Karakayali H (2006) Turkey	*	*	*	*	**	*			7
Sotiropoulos GC (2007) Germany	*	*	*	*	**	*	*	*	9
Fisher RA (2007) USA	*	*	*	*	**	*	*	*	9
Terrault NA (2007) USA	*	*	*	*	**	*			7
Allam N (2008) KSA	*	*	*	*	*	*	*	*	8
Di Sandro S (2009) Italy	*	*	*	*	*	*	*	*	9
Vakili K (2009) USA	*	*	*	*		*	*	*	7
Berg CL (2011) USA	*	*	*	*	*	*	*	*	8
Bhangui P (2011) France	*	*	*	*	**	*	*	*	9
Azzam AZ (2011) KSA	*	*	*	*	*	*	*		7
Kulik LM (2012) USA	*	*	*	*	**	*	*	*	9
Sandhu L (2012) Canada	*	*	*	*	**	*	*	*	9
Li C (2013) China	*	*	*	*	**	*	*	*	9
Lei J (2013) China	*	*	*	*	**	*	*	*	9
Xiao GQ (2014) China	*	*	*	*	*	*	*		7
Chen J (2014) China	*	*	*	*	*	*	*		7
Park MS (2014) Korea	*	*	*	*	**	*	*	*	9
Wan P (2014) China	*	*	*	*	**	*	*	*	9
Bonadio I (2014) Belgium	*	*	*	*	*	*	*		7
Ninomiya M (2015) Japan USA	*	*	*	*	*	*	*	*	8
Chen LP (2015) China	*	*	*	*	**	*	*		8
Azoulay D (2017) France	*	*	*	*	**	*	*	*	9
Goldaracena N (2019) Canada	*	*	*	*	*	*	*	*	8
Wong TCL (2019) China	*	*	*	*	**	*	*	*	9
Lee S (2020) Korea	*	*	*	*	**	*	*	*	9
Rahatli S (2020) Turkey	*	*	*	*		*	*	*	7

* stands for one point

** stands for two points