Table 1.
Subgroup analysis for the contribution of outdoor air pollution to COPD mortality *.
| Category | Study Characteristics (Number of Studies) | Summary Estimate | Summary Estimate | I2 |
|---|---|---|---|---|
| Study design | Cohort (2) | 1.11 | 1.07~1.15 | 0%# |
| Case crossover (3) | 1.01 | 1.00~1.01 | 42%# | |
| Ecological study (8) | 1.02 | 1.01~1.03 | 57% | |
| Cross sectional (1) | 1.09 | 1.06~1.12 | NA | |
| Research field | EU (4) | 1.07 | 1.04~1.11 | 0%# |
| US (4) | 1.03 | 1.00~1.06 | 84% | |
| China (4) | 1.01 | 1.00~1.01 | 3%# | |
| others (2) | 1.06 | 1.02~1.11 | 87% | |
| PM size | PM10 (11) | 1.02 | 1.01~1.04 | 76% |
| TSP (3) | 1.07 | 1.01~1.13 | 79% | |
| PM increment | PM10 10 ug/m3 increment (8) | 1.02 | 1.01~1.03 | 76% |
| Others (6) | 1.08 | 1.04~1.12 | 58% | |
| The effect of 10 ug/m3 PM10 increment in different areas | China (3) | 1.01 | 1.00~1.01 | 0%# |
| US (3) | 1.03 | 1.00~1.06 | 87% | |
| EU (1) | 1.04 | 0.99~1.06 | NA | |
| Others (1) | 1.04 | 1.02~1.06 | NA | |
| Effect duration | Chronic effect (3) | 1.10 | 1.07~1.12 | 0%# |
| Acute effect (11) | 1.02 | 1.01~1.03 | 59% | |
| Acute effects in different areas | China (4) | 1.01 | 1.00~1.01 | 3%# |
| EU (3) | 1.06 | 1.02~1.11 | 0%# | |
| US (3) | 1.01 | 1.01~1.02 | 56%# |
* The significance level for heterogeneity was 0.05; # non-significant.