• Epidemiology
• Allergy
• Asthma
• Air pollution

This issue of OEM reports the results of an ecological study (see page 293) using the GMAPS model to assess the association between the urban background concentration of PM₁₀ (particulate matter below an aerodynamic diameter of 10 μm) for 304 communities in 55 countries and ISAAC Phase One data on symptoms for atopic diseases and diagnoses for asthma, hay fever and eczema.1 The aim of this study was to investigate the role of ambient particulate matter in explaining geographical variation in the prevalence of asthma, rhinoconjunctivitis and eczema using the data of approximately half a million children worldwide. As the authors note, there was a weak negative association between PM₁₀ and the various outcomes. In 24 countries with more than one centre, most of the summary estimates for within-country associations were weakly positive. Anderson and colleagues conclude that urban background PM₁₀ has little or no association with the prevalence of childhood asthma, rhinoconjunctivitis or eczema either within or between countries. The conclusions are generally supported by the cited study results and the authors provide an excellent discussion of several crucial issues of importance when interpreting the data from this ecological study.

Nevertheless, the conclusions have to be read very carefully in order to avoid misinterpretation of the results presented. This study refers only to background PM₁₀, which is assumed to …