Garcia-Aymerich, J. Puhan, M.A. Corriol-Rohou, S. De Jong, C. Demeyer, H. Dobbels, F. Erzen, D. Frei, A. Gimeno-Santos, E. Hopkinson, N.S. Ivanoff, N. Karlsson, N. Louvaris, Z. Polkey, M.I. Rabinovich, R.A. Scuri, M. Tabberer, M. Vogiatzis, I. Troosters, T., Validity and responsiveness of the Daily-and Clinical visit-PROactive Physical Activity in COPD (D-PPAC and C-PPAC) instruments, Thorax, (76), 228-238, 2021, BMJ Publishing Group, 0040-6376, 1468-3296