Subgroup analysis on pooled ORs for the association between cigarette smoking and nasopharyngeal carcinoma
| Subgroup | No. of studies | Effect estimate (95% CI) | Heterogeneity I2 , p | Egger’s test p Value | Adjusted for publication bias |
| Smoking status | |||||
| Ever smokers | 19 | 1.56 (1.32 to 1.83) | 66.8%, <0.01 | 0.29 | 1.56 (1.32–1.84) |
| Current smokers | 11 | 1.59 (1.35 to 1.89) | 32.5%, 0.14 | 0.10 | |
| Former smokers | 10 | 1.36 (1.15 to 1.61) | 2.3%, 0.42 | 0.97 | |
| Design | |||||
| Case–control | |||||
| Current smokers | 8 | 1.67 (1.06 to 2.61) | 22.6%, 0.25 | 0.58 | |
| Former smokers | 8 | 1.45 (1.21 to 1.73) | 0.0%, 0.70 | 0.98 | |
| Cohort | |||||
| Current smokers | 3 | 2.19 (1.02 to 4.72) | 65%, 0.06 | 0.16 | |
| Former smokers | 2 | 0.87 (0.54 to 1.41) | 0.0%, 0.37 | ─ | |
| Pack-years | |||||
| <30 | 7 | 1.34 (1.13 to 1.58) | 0.0%, 0.73 | 0.54 | |
| ≥30 | 6 | 2.03 (1.57 to 2.61) | 0.0%, 0.45 | <0.01 | 1.80 (1.37–2.36) |
| Age at onset of smoking (years) | |||||
| <18 | 5 | 1.78 (1.41 to 2.25) | 0.0%, 0.94 | 0.46 | |
| ≥18 | 5 | 1.28 (1.00 to 1.64) | 0.0%, 0.86 | 0.93 | |
| Incidence rate | |||||
| Low | 5 | 1.68 (1.36 to 2.07) | 0.0%, 0.84 | 0.64 | |
| Intermediate | 10 | 1.59 (1.21 to 2.09) | 78.8%, <0.01 | 0.29 | |
| High | 4 | 1.27 (1.05 to 1.53) | 0.0%, 0.52 | 0.63 | |
| Gender | |||||
| Man | 5 | 1.36 (1.15 to 1.60) | 0.0%, 0.68 | 0.48 | |
| Woman | 2 | 1.58 (0.99 to 2.53) | 0.0%, 0.64 | ─ | |
| Histological type | |||||
| Differentiated | 5 | 2.34 (1.77 to 3.09) | 0.0%, 0.72 | 0.64 | |
| Undifferentiated | 4 | 1.15 (0.90 to 1.46) | 0.0%, 0.02 | 0.28 | |
| Adjustment | |||||
| Adjusted | 13 | 1.55 (1.26 to 1.91) | 75.4%, <0.01 | 0.33 | |
| Unadjusted | 6 | 1.57 (1.27 to 1.93) | 0.0%, 0.68 | 0.93 |