General characteristics of case–control studies used for meta-analysis
| Study | Region | Period | Incidence rate | Cases /Controls | Man /Woman | Age range (years old) | Quality score | Source of controls | Matching factors | Adjusting factors |
| Mabuchi et al 34 | USA | – | Low | 39/39 | – | – | 7 | Hospital-based | Age, sex, race, Education, occupation, marital status | ─ |
| Yu et al 37 | Guangzhou | 1983–1985 | High | 306/306 | 209/97 | Under 45 | 7 | Population-based | Age, sex, residence, education | Birth place, marital status, dietary risk |
| Nam et al 35 | USA | 1983–1986 | Low | 204/408 | 141/63 | <65 | 5 | Hospital-based | Age, sex | By multiple logistic regression analysis |
| Sriamporn et al 36 | Thailand | 1987–1990 | Moderate | 120/120 | 81/39 | Mean 47.2 | 6 | Hospital-based | Age, sex | Age, sex, education, residence, occupation, consumption of salted fish and alcohol |
| Zhu et al 38 | USA | 1984–1988 | Low | 113/1910 | Man | – | 8 | Population-based | ─ | Birth, education, background, medical history, occupation, alcohol intake |
| Vaughan et al 39 | USA | 1987–1993 | Low | 231/244 | 154/77 | Mean 55.2 | 9 | Population-based | Age, sex, region | Age, sex, alcohol use, education |
| Cheng et al 7 | Taiwan | 1991–1994 | Moderate | 375/327 | 260/115 | Mean 46 (15–74) | 7 | Population-based | Age, sex, residence, education, marital status | Age, sex, race, education, family history of NPC, drinking status |
| Chelleng et al 40 | India | 1996–1997 | Moderate | 47/94 | 34/13 | Mean 43.7 | 6 | Population-based | Age, sex, ethnicity | ─ |
| Yuan et al 41 | Shanghai | 1987–1991 | Moderate | 935/1032 | 668/267 | Mean 50 | 8 | Population-based | Age, sex, residence | Age, gender, education, intake frequencies of preserved foods, occupational exposure history of chronic ear and nose condition, family history of NPC |
| Zou et al 51 | Yangjiang | 1987–1995 | High | 97/192 | 83/14 | Mean 52.6 (30–82) | 7 | Population-based | Age, sex, occupation | ─ |
| Feng et al 42 | North Africa | 2002–2005 | Moderate | 440/409 | Man | – | 7 | Hospital-based | Age, sex, ethnicity, centre, childhood household type | Age, socioeconomic status, dietary risk factors |
| Ji et al 44 | Wuhan | 1991–2009 | Moderate | 1044/1095 | 755/289 | – | 5 | ─ | Age, sex, ethnicity | Age, gender, cigarette, alcohol intake, family history |
| Polesel et al 9 | Italy | 1992–2008 | Low | 150/450 | 119/31 | Median 52 (18–76) | 6 | Hospital-based | Age, sex, residence | Age, sex, place of residence, education, alcohol intake |
| Turkoz et al 45 | Turkey | – | Moderate | 183/183 | 122/61 | Mean 44.9 (18–75) | 6 | Hospital-based | Age, sex | Age, sex |
| Fachiroh et al 23 | Thailand | 2005–2010 | Moderate | 681/1078 | 504/177 | Mean 49.8 | 6 | Hospital-based | Age, sex, residence | Age group, sex, centre, education, alcohol drinking |
| Lye et al 25 | Malaysia | 2007 | Moderate | 356/356 | 276/80 | Mean 53.2 | 6 | Hospital-based | Age, sex, ethnicity | Age, sex, ethnicity, salted fish and alcohol intake |
| Xie et al 26 | Hong Kong | 2010–2012 | High | 352/410 | 253/99 | Mean 51.6 | 8 | Population-based | Age, sex, ethnicity, residence district | Age, sex, education, house type, family history of NPC, environmental tobacco smoke exposure, dietary risk, occupational exposure and cooking experience |
NPC, nasopharyngeal carcinoma.