* Meta-analysis results from refere

* Meta-analysis results from reference 19, unless otherwise stated.
† Strong evidence: Some 15–20 observational studies for each condition, from
developing countries. Evidence is consistent (significantly elevated risk in most,
although not in all, studies); the effects are sizable, plausible, and supported
by evidence from outdoor air pollution and smoking.19
‡ Small number of studies, not all consistent (especially for asthma, which
may reflect variations in definitions and condition by age), but supported by
studies of outdoor air pollution, smoking, and laboratory animals.19
§ Insufficient for quantification based on available evidence.19
RR = relative risk; CI = confidence interval.