Association between outdoor PM 2.5 and prevalence of COPD: a systematic review and meta-analysis

There were conflictions and differences among the results of cross-sectional studies association between PM and COPD prevalence. We aimed to explore the real association between outdoor PM and COPD prevalence, analyze the possible cause to the differences and conflictions in previous cross-sectional studies. Cross-sectional literatures about the association between outdoor PM and COPD prevalence were selected up to 12 September 2018. Subgroup analysis was performed to explore the source of the heterogeneity. Publication bias was tested via funnel plot. Leave-one-out method was used to conduct influential analysis. Variance analysis was used to analyze the influence of concentration, literature quality and age (over 60 or not) on the ln (aOR) values. The initial search revealed 230 studies, of which 8 were selected. The heterogeneity in this study was significant (I =62, P