While the definitions of cases and controls within each study – based on GOLD criteria – were similar, COPD is a highly heterogeneous disease, and differences exist between the studies 47. To explore these considerations, we used alternative methods for meta-analysis based on modified random-effects and binary effects model that may be more powerful in the presence of heterogeneity among studies48,49 (see Supplement). However, we were not able to identify new genome-wide significant results using these methods.
