Table 2.

Newcastle–ottawa quality assessment scale for cohort studies

References	Selection	Comparability	Outcome			Total score
			Assessment of outcome	Follow-up long enough for outcomes	Adequacy of follow-up of cohorts
Panagopoulos et al. (2001)	4	2	0	0	0	6
Mezzelani et al. (2001)	4	2	0	0	1	7
Ladanyi et al. (2002)	4	2	1	0	1	8
Guillou et al. (2004)	4	2	1	0	1	8
Takenaka et al. (2008)	4	2	1	0	0	7
ten Heuvel et al. (2009)	4	2	0	0	0	6
Sun et al. (2009)	4	2	0	0	0	6
Krieg et al. (2011)	4	2	0	1	1	8
Charbonneau et al. (2013)	4	2	0	0	0	6
Ren et al. (2013)	4	2	0	0	0	6