Variability of FVC and FEV1 due to technician, team, device and subject in an eight centre study: three quality control studies in SAPALDIA. Swiss Study on Air Pollution and Lung Disease in Adults. - Kunzli,N.; Ackermann-Liebrich,U.; Keller,R.; Perruchoud,A.P.; Schindler,C. (Eur Respir J, 1995)