TABLE 1.
Pooled relative risk and corresponding 95% confidence interval of lung cancer for never-smokers exposed to second-hand smoke (SHS) versus nonexposed to SHS, overall and in strata of selected characteristics
| Strata | Number of studies | Pooled relative risk (95% CI) | p-value# | p-value¶ |
|---|---|---|---|---|
| Total | 82 | 1.24 (1.16–1.32) | NA | <0.01 |
| Settings of SHS exposure | ||||
| At home+ | 67 | 1.20 (1.12–1.28) | NA | <0.01 |
| At workplace | 30 | 1.38 (1.28–1.62) | <0.01 | |
| At home or workplace | 28 | 1.37 (1.22–1.53) | <0.01 | |
| Nonspecified | 24 | 1.27 (1.11–1.44) | <0.01 | |
| Specific sources | ||||
| From partner | 41 | 1.18 (1.08–1.29) | NA | <0.01 |
| During childhood | 34 | 1.12 (1.00–1.26) | <0.01 | |
| Sex | ||||
| Male | 15 | 1.15 (0.96–1.37) | 0.66 | 0.67 |
| Female | 51 | 1.20 (1.11–1.29) | 0.04 | |
| Subtypes | ||||
| NSCLC | 26 | 1.43 (1.24–1.65) | NA | <0.01 |
| Adenocarcinoma | 23 | 1.42 (1.21–1.67) | <0.01 | |
| SQCLC | 7 | 1.98 (1.57–2.49) | 0.38 | |
| LCLC | 2 | 1.69 (0.92–3.09) | 0.49 | |
| SCLC | 5 | 1.99 (1.17–3.39) | 0.10 | |
| Geographic area§ | ||||
| Northern and Central America | 19 | 1.12 (1.01–1.24) | 0.02 | 0.52 |
| Europe | 16 | 1.08 (0.97–1.21) | 0.57 | |
| Asia | 42 | 1.33 (1.21–1.46) | <0.01 | |
| Oceania | 2 | 1.05 (0.73–1.51) | 0.30 | |
| Income group## | ||||
| High-income | 57 | 1.19 (1.09–1.29) | 0.23 | <0.01 |
| Middle-income | 25 | 1.31 (1.14–1.51) | <0.01 | |
| Study design | ||||
| Case–control | 57 | 1.30 (1.20–1.41) | <0.01 | <0.01 |
| Cohort | 25 | 1.07 (0.99–1.16) | 0.75 | |
| Type of controls¶¶ | ||||
| Hospital | 15 | 1.30 (1.13–1.49) | 0.87 | <0.01 |
| Population | 35 | 1.28 (1.13–1.45) | <0.01 | |
| End-point++ | ||||
| Incidence | 14 | 1.15 (1.02–1.30) | 0.19 | 0.46 |
| Mortality | 13 | 1.03 (0.93–1.14) | 0.77 | |
| Year of publication | ||||
| <1998 | 26 | 1.20 (1.07–1.35) | 0.85 | 0.38 |
| 1998–2009 | 27 | 1.22 (1.10–1.36) | 0.05 | |
| ≥2010 | 29 | 1.26 (1.13–1.40) | <0.01 | |
| Adjustment | ||||
| Crude | 10 | 1.12 (0.95–1.31) | 0.28 | 0.09 |
| Adjusted | 72 | 1.23 (1.14–1.33) | <0.01 | |
| Number of cases | ||||
| ≤89 | 28 | 1.34 (1.16–1.55) | 0.15 | 0.38 |
| 90–219 | 26 | 1.33 (1.18–1.49) | 0.12 | |
| ≥220 | 28 | 1.17 (1.07–1.28) | <0.01 | |
| Study quality | ||||
| Low (NOS <7) | 62 | 1.25 (1.16–1.35) | 0.68 | <0.01 |
| High (NOS ≥7) | 20 | 1.21 (1.08–1.37) | <0.01 | |
#: p-value for heterogeneity across strata. ¶: p-value for heterogeneity within strata. +: Including exposure from partner. §: No studies from Africa or South America. ##: No studies from low-income countries. ¶¶: Type of controls for case–control studies only. ++: End-point for cohort studies only. LCLC: large-cell lung cancer; NA: not applicable; NOS: Newcastle Ottawa Scale; NSCLC: nonsmall-cell lung cancer; SCLC: small-cell lung cancer; SQCLC: squamous-cell lung cancer.