Changes in responder classification and corresponding subgroup mean FEV1 at each visit after both bronchodilators using (A) American Thoracic Society and (B) European Respiratory Society criteria. Changes in responder classification and corresponding subgroup mean FEV1 at each visit after both bronchodilators using (A) American Thoracic Society and (B) European Respiratory Society criteria. Numbers in circles refer to the total classified as positive responders at that visit and those in squares are the non-responders on the same occasion. Note that some patients in the ERS criteria group exhibited a “response” after both drugs at the first visit despite being classified as non-responsive to salbutamol alone. P M A Calverley et al. Thorax 2003;58:659-664 Copyright © BMJ Publishing Group Ltd & British Thoracic Society. All rights reserved.