Table 1. Characteristics of studies included in the meta-analysis.
| First Author | Publication Year | Number of Cases (male/female) | Number of Controls (male/female) | Type of controls | Mean age, year Cases/Controls | Racial decent | Types | Country | Ref No. |
|---|---|---|---|---|---|---|---|---|---|
| Weinstein | 2002 | 519 (NA/NA) | 629 (NA/NA) | Healthy controls (Age-, gender- matched; population-based) | 63.2/61.0 | Caucasian | Oral cavity | USA | 43 |
| Kureshi | 2004 | 50 (33/17) | 54 (30/24) | Healthy controls (Age-, gender- matched; population-based) | 51.3/50.2 | Mixed | Combined | Pakistan | 28 |
| Capaccio | 2005 | 65 (57/8) | 100 (88/12) | Healthy controls (Age-, gender-, drinking-, smoking status- matched; population-based) | 61.3/58.8 | Caucasian | Combined | Italy | 23 |
| Neumann | 2005 | 537 (411/126) | 545 (401/144) | Non-cancerous controls (Age-,sex-, smoking status-matched; hospital-based) | NA/NA | Caucasian | Combined | USA | 29 |
| Vairaktaris | 2006 | 110 (94/16) | 120 (102/18) | Healthy controls (Age-, sex, ethnicity-matched; population-based) | 52.1/51.5 | Caucasian | Oral cavity | GreekGerman | 41 |
| Hsiung | 2007 | 278 (193/85) | 526 (377/149) | Healthy controls (Age-, gender, town of residence-matched; population-based) | 60.1/61.0 | Mixed | Combined | USA | 26 |
| Reljic | 2007 | 81 (NA/NA) | 102 (37/65) | Healthy controls (Age-matched; population-based) | NA/NA | Caucasian | Combined | Croatia | 33 |
| Suzuki | 2007 | 237 (188/49) | 711 (564/147) | Non-cancerous controls (Age-,sex-matched; hospital-based) | 57.9/58.4 | Asian | Combined | Japan | 39 |
| Ni | 2008 | 207 (189/18) | 400 (362/38) | Healthy controls (Age-,sex-matched; population-based) | NA/NA | Asian | Larynx | China | 30 |
| Siraj | 2008 | 223 (NA/NA) | 513 (NANA) | Healthy controls (Age-matched; population-based) | NA/NA | Mixed | Thyroid | Saudi Arabia | 36 |
| Solomon | 2008 | 126 (NA/NA) | 100 (NA/NA) | Healthy individuals(population-based) | 54.7/55.4 | Asian | Oral cavity | India | 37 |
| Cao | 2010 | 529 (339/190) | 577 (367/210) | Healthy controls (Age-,sex-, ethnicity-matched; population-based) | 46.1/45.4 | Asian | Nasopharynx | China | 22 |
| Kruszyna | 2010 | 131 (131/0) | 250 (250/0) | Healthy controls (population-based) | 59.4/56.8 | Caucasian | Larynx | Poland | 27 |
| Rodrigues | 2010 | 100 (84/16) | 100 (76/24) | Non-cancerous controls (hospital-based) | 59.5/43.6 | Mixed | Combined | Brazil | 34 |
| Fard-Esfahani | 2011 | 154 (34/120) | 198 (50/148) | Non-cancerous controls (hospital-based) | NA/NA | Mixed | Thyroid | Iran | 24 |
| Prasad | 2011 | 97 (27/70) | 241 (116/125) | Healthy controls (population-based) | NA/NA | Asian | Thyroid | India | 32 |
| Sailasree | 2011 | 130 (88/42) | 139 (92/47) | Non-cancerous controls (Age-,gender-matched; hospital-based) | 58.0/57.0 | Asian | Oral cavity | India | 35 |
| Supic | 2011 | 96 (72/24) | 162 (130/32) | Non-cancerous controls(Age-, gender-, ethnicity-matched; population-based) | 58.0/58.0 | Caucasian | Oral cavity | Serbia | 38 |
| Tsai | 2011 | 620 (583/37) | 620 (572/48) | Healthy controls (Age-, gender-, habits-matched; population-based) | 65.5/63.5 | Asian | Oral cavity | China | 40 |
| Galbiatti | 2012 | 322 (280/42) | 531 (384/147) | Healthy controls (population-based) | NA/NA | Mixed | Combined | Brazil | 25 |
| Ozdemir | 2012 | 60 (11/49) | 50 (21/29) | Healthy controls (population-based) | 55.3/68.6 | Mixed | Thyroid | Turkey | 31 |
| Vylliotis | 2013 | 160 (NA/NA) | 168 (NA/NA) | Healthy controls (Age-, gender-, ethnicity-, working environment-matched; population-based) | 58.5/54.7 | Caucasian | Oral cavity | Greece | 42 |
| Kweon | 2014 | 2194 (404/1790) | 1669 (812/857) | Healthy controls (Age-, gender-, matched; population-based) | 50.6/52.2 | Asian | Thyroid | Korea | 44 |
NA: not available