Table 2.
Subgroup analysis for the contribution of outdoor air pollution to hospital admission for COPD *.
| Category | Study Characteristics (Number of Studies) | Summary Estimate | Summary Estimate | I2 |
|---|---|---|---|---|
| Study Design | Case-crossover (4) | 1.11 | 1.00 ~ 1.23 | 84% |
| Ecological study (23) | 1.02 | 1.01 ~ 1.02 | 64% | |
| Research Field | US (10) | 1.02 | 1.01 ~ 1.03 | 71% |
| EU (8) | 1.02 | 1.01 ~ 1.04 | 61% | |
| China (5) | 1.01 | 1.01 ~ 1.02 | 80% | |
| Others (4) | 1.05 | 1.02 ~ 1.08 | 46% # | |
| PM size | PM10 (19) | 1.02 | 1.01 ~ 1.02 | 72% |
| Others (8) | 1.02 | 1.01 ~ 1.03 | 60% | |
| PM increment | PM10 10 ug/m3 increment (9) | 1.01 | 1.01 ~ 1.01 | 16% # |
| Others (18) | 1.03 | 1.02 ~ 1.05 | 75% | |
| The effect of 10 ug/m3 PM10 increment in different areas | china (3) | 1.01 | 1.01 ~ 1.01 | 46% # |
| US (4) | 1.02 | 1.01 ~ 1.03 | 0% # | |
| EU (2) | 1.01 | 1.00 ~ 1.02 | 59% # |
* The significant level for heterogeneity was 0.05; # non-significant.