RT Journal
A1 Mustafić H, Jouven X, Jabre P
T1 EXposure to air pollutants and myocardial infarction risk—reply
JF JAMA
JO JAMA
YR 2012
FD June 13
VO 307
IS 22
SP 2370
OP 2370
DO 10.1001/jama.2012.4118
UL http://dx.doi.org/10.1001/jama.2012.4118
AB 
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