Lung function was measured with meticulousness in both studies but differs primarily, because the test was performed post bronchodilation in ECLIPSE and without bronchodilation in DLCST. We believe that this has negligible effect because ECLIPSE is a specialist center cohort and most of the participants were on standard of care, the opposite was true for the populationbased DLSCT cohort. CT protocols and image analysis software differed between DLCST and ECLIPSE, and CT quantification of emphysema is influenced by both scan parameters (such as slice thickness and reconstruction algorithm) and choice of software. However, previous studies of CT quantification of emphysema have shown minimal differences between results obtained with soft reconstruction (DLCST) and an intermediate spatial frequency reconstruction (ECLIPSE).52