Circulating tumor cells as potential prognostic biomarkers for early-stage pancreatic cancer: A systematic review and meta-analysis

Table 2 Quality assessment of the included studies according to the Newcastle-Ottawa Scale criteria for non-randomized studies

Ref.	Selection				Comparability			Outcome		Total stars
	Representativeness	Selection of non-exposed	Ascertainment of exposure	Outcome not present at start	Comparability on most important factors	Comparability on other risk factors	Assessment of outcome	Long enough follow-up (median ≧ 24 mo)	Completeness of follow-up
Xing et al[14]	-	1	1	1	1	-	1	-	1	6
Semaan et al[15]	-	1	1	1	1	-	1	-	1	6
Padillo-Ruiz et al[21]	-	1	1	1	1	-	1	1	1	7
Court et al[16]	-	1	1	1	1	-	1	1	1	7
Cheng et al[17]	1	1	1	1	1	-	1	-	1	7
White et al[18]	-	1	1	1	1	-	1	-	1	6
Bissolati et al[19]	1	1	1	1	1	-	1	1	1	8
Hugenschmidt et al[20]	-	1	1	1	1	-	1	1	1	7

¹Meets the criteria of the scale. A maximum of one ‘star’ for each item within the ‘Selection’ and ‘Outcome’ categories; maximum of two ‘stars’ for ‘Comparability’; -Does not meet the criteria of the scale.