Author Affiliations: Paris Cardiovascular Research Center, University Paris Descartes, Paris, France (firstname.lastname@example.org).
In Reply: We agree with Mr Huang and Dr Mao that there is heterogeneity among studies evaluating the effect of air pollutants on the risk of MI. The intent in performing a meta-analysis is, as far as possible, to reduce heterogeneity. We converted the pollutant concentrations from the various studies to the same units and chose the most frequently used values for the increase in pollutant concentrations: 10 μg/m3 for all pollutants except for carbon monoxide and 1 mg/m3 for carbon monoxide. This method is frequently used for meta-analyses.1
Mustafić H, Jouven X, Jabre P. Exposure to Air Pollutants and Myocardial Infarction Risk—Reply. JAMA. 2012;307(22):2370. doi:10.1001/jama.2012.4118