Fig. 1

Aggregated topics indexed along with asthma. The figure is based on the aggregated indexed topics which are presented in the same clockwise order as listed in Additional file 1: Table S2. Bubble diameter is proportional to the number of systematic reviews with the respective index term (this number is based on all n = 421 systematic reviews on allergy epidemiology, also non-asthma systematic reviews (based on the aggregated disease index term “asthma”), included in our previous overview [8]). Line thickness is proportional to the number of systematic reviews indexed with the connected index terms. Colours are arbitrary, covering the spectrum from blue to red in clockwise order