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*FEV1/FVC ratio <0.7
**The previous version of this review included both RCTs and non‐RCTs
#References included full‐text articles, trial register abstracts, conference abstracts, and sub‐studies
##One study could not be included in any meta‐analyses because of insufficient available data
RCT: Randomised controlled trial; CRT: Cluster‐randomised controlled trial
