To enable a head-to-head comparison between our findings and those of Sievi and colleagues, the cohort, test methodology, reference values and cut points to classify patients in the ‘can do, do do’ quadrants needs to be similar. In our study, we included COPD patients upon first referral to secondary pulmonary care, while the cohort of Sievi et al. comprised of patients already in secondary care. This may have led to the selection of a more severely impaired cohort in the Swiss study, which, compared to our study, is indeed reflected in a lower mean FEV
1 (44 versus 56%pred), a lower median physical activity level (4421 versus 5112 steps/day), and a lower median 6-min walking distance (6MWD; 418 versus 440 m, respectively). Then it would not surprise if quadrant representation would differ between the studies, where we anticipated that Sievi’s study have proportionally more patients in the “can’t do” quadrants and less in the “can do” quadrants. However, the opposite is true. Sievi’s cohort had only 35% of patients in the “can’t do” quadrants versus 55% in our study, and as much as 65% in the “can do” versus 45% in our study. This discrepancy can probably be explained on the basis of 6MWD reference values. While we applied the Troosters’ reference values [
4], Sievi and colleagues used those of Enright [
5] of which we know that they significantly overestimate exercise capacity [
6]. This has likely caused the shift in ‘can do’ – ‘can’t do’ proportions and precludes true comparison with our study. Considering this 6MWD reference is a key factor in the ‘can do, do do’ concept, we are curious to learn how this would alter the proportions and characteristics of the quadrants in Sievi’s cohort. Moreover, we anticipate that the graph in Figure 2 mistakenly puts the PA cut point at 75% as opposed to the proposed 70%.