Table 2.

The assessment of the risk of bias in each Cohort study using the Newcastle-Ottawa scale

Study	Selection (0-4)				Comparability(0-2)		Outcome (0-3)			Total
	REC	SNEC	AE	DO	SC	AF	AO	FU	AFU
Sotelo 2014 [24]	*	*	*	*	-	-	*	*	-	6
Seeberg 2014 [25]	*	*	*	*	-	-	*	*	*	7
Gazzaniga 2013 [26]	-	*	*	*	-	-	*	-	-	4
Aggarwal 2013 [27]	-	*	*	*	-	-	*	*	-	5
Kuboki 2013 [14]	-	*	*	*	-	-	*	*	-	5
Deneve 2013 [13]	-	*	*	*	-	-	*	*	-	5
Sastre 2012 [28]	*	*	*	*	-	-	*	*	-	6
Sato 2012 [29]	*	*	*	*	-	-	*	-	-	5
Papavasiliou 2010 [30]	-	-	*	*	-	-	*	-	-	3
Tol 2010 [31]	*	*	*	*	-	-	*	-	-	5
Hiraiwa 2008 [15]	-	*	*	*	-	-	*	-	-	4

NOTE. REC: representativeness of the exposed cohort; SNEC: selection of the non-exposed cohort; AE: ascertainment of exposure; DO: demonstration that outcome of interest was not present at start of study; SC: study controls for age, sex; AF: study controls for any additional factors (chemoradiotherapy, curative resection); AO: assessment of outcome; FU: follow-up long enough (36M) for outcomes to occur; AFU: adequacy of follow-up of cohorts (≥90%).'*' means that the study is satisfied the item (high quality with no bias), and '-' means that the study is not satisfied the item (low quality with bias); Total: the number of high-quality items (no bias) in each study.