Table 4.
Results of the Meta-Analyses of Studies of Childhood Leukemia and Traffic Density, Traffic-Related Air Pollution Models, or Gas Station Residential Proximity, 1999–2014
| Group and Subgroup | No. of Studies | Fixed Effects |
Shore-Adjusteda |
Random Effectsa |
Heterogeneity |
|||
|---|---|---|---|---|---|---|---|---|
| sRR | 95% CI | 95% CI | sRR | 95% CI | χ2 | P Value | ||
| Outcome | ||||||||
| All studies combined | 12 | 1.48 | 1.23, 1.78 | 1.10, 1.99 | 1.80 | 1.29, 2.52 | 27.49 | <0.01 |
| AML only | 4 | 2.07 | 1.34, 3.20 | NA | NA | NA | 0.40 | 0.94 |
| ALL only | 7 | 1.49 | 1.20, 1.84 | 1.07, 2.08 | 1.79 | 1.21, 2.65 | 14.96 | 0.02 |
| Exposure metric | ||||||||
| Traffic density | 11 | 0.97 | 0.88, 1.07 | 0.82, 1.15 | 1.25 | 0.96, 1.62 | 29.92 | <0.01 |
| Traffic density (excluding Heck et al. (85))b | 10 | 1.17 | 0.99, 1.40 | 0.89, 1.55 | 1.38 | 0.96, 1.62 | 23.26 | 0.01 |
| Traffic pollution models (e.g., CALINE4)c | 7 | 1.70 | 1.25, 2.30 | 1.16, 2.49 | 1.77 | 1.17, 2.68 | 9.38 | 0.15 |
| Adjustmentsd | ||||||||
| Socioeconomic status | 9 | 1.49 | 1.19, 1.86 | 1.07, 2.08 | 1.77 | 1.20, 2.62 | 18.05 | 0.02 |
| Area | ||||||||
| Europe | 8 | 1.35 | 1.09, 1.68 | 0.95, 1.93 | 1.65 | 1.09, 2.52 | 19.51 | 0.01 |
| United States | 4 | 2.02 | 1.35, 3.00 | 1.20, 3.38 | 2.13 | 1.25, 3.64 | 5.02 | 0.17 |
| Time of exposure | ||||||||
| Birth or gestation only | 4 | 0.92 | 0.75, 1.14 | 0.73, 1.17 | 0.94 | 0.73, 1.22 | 3.93 | 0.27 |
| Postnatal (any) | 13 | 1.36 | 1.15, 1.60 | 1.05, 1.76 | 1.59 | 1.19, 2.13 | 29.19 | <0.01 |
| At diagnosis only | 9 | 1.46 | 1.19, 1.80 | 1.03, 2.08 | 1.94 | 1.30, 2.91 | 22.91 | <0.01 |
| Residential proximity to gas stations | 3 | 1.59 | 0.95, 2.67 | 0.70, 3.62 | 1.88 | 0.78, 4.55 | 5.08 | 0.08 |
Abbreviations: ALL, acute lymphoblastic leukemia; AML, acute myeloid leukemia; CALINE4, California LINE Source Dispersion Model, version 4; CI, confidence interval; NA, not applicable; sRR, summary relative risk.
a The Shore-adjusted and random-effects models were used if the χ2 statistic was greater than the degrees of freedom (the number of studies minus 1).
b Heck et al. (85) contributed 69% of the total weight in the traffic-density analysis.
c Includes studies with more detailed modeling of traffic pollution or ambient air levels of benzene.
d Includes adjusted results and results from studies in which the authors stated that the adjustments had little or no impact on results. Few of these studies were adjusted for tobacco smoking.