Table 2. Quality assessment of eligible studies using the Newcastle-Ottawa Scale (NOS).

First author, year	Represen tativeness of exposed cohort	Selection of non exposed cohort	Ascer tainment of exposure	Demonstration that outcome was not present at start of study	Comparability based on the design or analysis	Assessment of outcome	Follow-up long enough for outcomes to occur	Adequacy of follow-up of cohorts	Total NOS score (stars)
NPC
Chen, 2010	1	1	1	1	2	1	1	0	8
Hariwiyanto, 2010	1	1	1	1	2	1	0	0	7
Kitagawa, 2013	1	1	1	1	1	1	1	0	7
Li, 2009	1	1	1	1	2	1	1	0	8
Sarac, 2001	1	1	1	1	0	1	1	1	7
Song, 2007	1	1	1	1	1	1	1	1	8
Wang, 2008	1	1	1	1	1	1	1	1	8
Zhu, 2004	1	1	1	1	1	1	1	1	8
NHL
Cao, 2008	1	1	1	1	0	1	1	1	7
Hirose, 2006	1	1	1	1	1	1	0	0	6
Ishii, 2007	1	1	1	1	1	1	0	1	7
Kanemitsu, 2012	1	1	1	1	1	1	0	0	6
Kuze, 1996	1	1	1	1	0	1	0	0	5
Paydas, 2008	1	1	1	1	0	1	0	0	5
Xu, 2009	1	1	1	1	0	1	1	1	7
Yamamoto,1999	1	1	1	1	0	1	1	1	7
Zhao, 2005	1	1	1	1	0	1	1	1	7
HL
Clarke, 2001	1	1	1	1	0	1	1	0	6
Claviez, 2005	1	1	1	1	0	1	1	1	7
Dinand, 2009	1	1	1	1	0	1	1	1	7
Enblad, 1999	1	1	1	1	0	1	1	1	7
Engel, 2000	1	1	1	1	1	1	0	1	7
Glavina-Durdov, 2001	1	1	1	1	1	1	0	1	7
Herling, 2003	1	1	1	1	1	1	1	0	7
Keresztes, 2005	1	1	1	1	0	1	1	0	6
Krugmann, 2003	1	1	1	1	0	1	1	1	7
Morente, 1997	1	1	1	1	1	1	1	1	8
Murray, 1999	1	1	1	1	1	1	0	0	6
Naresh, 2000	1	1	1	1	0	1	1	0	6
Quijano, 2004	1	1	1	1	1	1	0	0	6
Stark, 2002	1	1	1	1	1	1	1	1	8
GC
Lee, 2004	1	1	1	1	0	1	1	0	6

Abbreviations: HL, Hodgkin lymphoma; NHL, non-Hodgkin lymphoma; NPC, nasopharyngeal carcinoma; GC, gastric cancer.