Table 1. Characteristics of Eligible Studies.
| First Author | Year | Country | Histological types | Source of controls | Mean age of case/control | Male (%) of case/control | Smoke(%) ofcase/control | NO. of cases | NO. of controls |
| Lan | 2000 | China | NA | PB | 55/55 | 64.8/64.8 | 100/100 | 122 | 122 |
| London | 2000 | China | NA | PB | NA/NA | NA/NA | NA/NA | 232 | 710 |
| Kiyohara | 2000 | Japan | SqCC = 27.9%, SCLC = 14.0%, AC = 46.5%, LCC = 4.7%, others = 7.0% | PB | 63.8/59 | 100/100 | 45.5/68.6 | 86 | 88 |
| Zhao | 2001 | Singapore | NA | HB | 65.5/63.6 | 0/0 | 41.2/9.6 | 233 | 187 |
| Sunaga | 2002 | Japan | AC = 100% | HB | 63/65 | 62.6/71.7 | 60.6/63.8 | 198 | 152 |
| Wang | 2003 | China | AC = 100% | PB | 56.5/54.5 | 64.3/66.4 | 42.9/66.4 | 112 | 119 |
| Liang | 2004 | China | SqCC = 41.4%, AC = 58.6% | HB | 60.5/60.5 | 70.4/70.4 | NA/NA | 152 | 152 |
| Sobti | 2004 | India | SqCC = 71.0%, SCLC = 24.0%, AC = 4.0%, LCC = 1.0% | PB | 55.5/50.9 | 95/96.1 | 86.0/77.6 | 100 | 76 |
| Chan | 2004 | China | SqCC = 16.6%, AC = 55.5%, others = 27.9% | PB | 53.8/49.3 | 67.2/59.4 | 56.8/40.1 | 229 | 197 |
| Yuan | 2005 | China | SqCC = 46.7%, AC = 40.7%, others = 12.7% | PB | 57.1/54.7 | 76.7/77 | 65.3/34.2 | 150 | 152 |
| Sreeja | 2005 | India | NA | PB | 58.2/56.1 | 91.1/87.7 | 59.9/45.2 | 146 | 146 |
| Chen | 2006 | China | SqCC = 52.6%, AC = 44.3%, others = 3.1% | PB | 56.6/55.8 | 43.3/48.7 | 0/0 | 97 | 197 |
| Lee | 2006 | Korea | SqCC = 43.3%, SCLC = 18.1%, AC = 28.1%, others = 10.5% | HB | 61/62.1 | 100/100 | 91.7/81.4 | 171 | 196 |
| Yang | 2007 | Korea | SqCC = 22.3%, SCLC = 9.7%, AC = 54.7%, others = 13.3% | PB | 55.4/48.3 | 67.6/61.8 | 62.3/50.1 | 318 | 353 |
| Sobti | 2008 | India | SqCC = 63.5%, SCLC = 15.8%, AC = 7.2%, others = 7.9% | HB | 56.9/56.4 | 86/81.4 | 81.4/74.2 | 151 | 151 |
| Sreeja | 2008 | India | NSCLC = 81.0%, SCLC = 9.5%, others = 9.5% | HB | 57.8/56.2 | 86.3/87.2 | 68.2/56.4 | 211 | 211 |
| Klinchid | 2009 | Thailand | SqCC = 39.6% AC = 60.4% | PB | 59.8/57.8 | 64/46 | 80.0/34.0 | 91 | 82 |
| Kumar | 2009 | India | SqCC = 23.0%, SCLC = 14.0%, AC = 38.0%, LCC = 6.0%, others = 20.0% | PB | 42.6/39.8 | 87.1/80.2 | 81.0/100 | 93 | 253 |
| Yadav | 2010 | India | NA | PB | 58/58 | 76.2/68.3 | 80.0/47.0 | 101 | 221 |
| Tamaki | 2011 | Japan | SqCC = 24.5%, SCLC = 21.4%, AC = 41.7%, LCC = 0.5%, others = 11.9% | HB | 80.3/80.3 | 67.2/69 | 70.3/51.7 | 192 | 203 |
| Fowke | 2011 | China | NA | PB | NA/NA | 0/0 | NA/NA | 209 | 787 |
| Kiyohara | 2012 | Japan | SqCC = 28.4%, SCLC = 14.9%, AC = 52.4%, LCC = 4.3% | HB | 66.1/55.9 | 62.1/74.7 | 66.9/44.8 | 462 | 379 |
| Wang | 2012 | China | SqCC = 49.3%, SCLC = 13.4%, AC = 33.0%, others = 4.3% | PB | 61.4/57.4 | 69.4/63.7 | NA/NA | 209 | 256 |
SqCC: squamous cell carcinoma; AC: adenocarcinoma; SCLC: small cell carcinoma; LCC: large cell carcinoma; NSCLC: non–small cell carcinoma; PB: population-based; HB: hospital-based.