The GOLD guideline2 threshold FEV1/FVC ratio of 70%, whether before or after bronchodilator administration, is deeply flawed. Despite good intentions, an invalid easy-to-remember number is still invalid. Miller et al1 add more data to what numerous committees and research reports have already emphasized3-11: GOLD categorization underdetects airway obstruction in many younger individuals and overdetects airway obstruction in many older individuals. Their report also reemphasizes the folly of using 80% predicted as a threshold to separate normal from abnormal for other pulmonary function parameters. It has been pointed out that absolute values (eg, FVC, FEV1, TLC) have moderate population variability, that ratios of volumes (eg, FEV1/FVC, FEV3/FVC, residual volume/TLC) have considerably lower population variability, and that flows divided by volumes (eg, forced expiratory flow, midexpiratory phase [FEF25%-75%]) have very high population variability.12 Although 80% predicted may be a somewhat defensible LLN value for FEV1, FEV6, and FVC for individuals between age 20 and 40, it is too high a value for older individuals. Eighty percent is also too high for FEV1/FVC or FEV3/FVC at any age and too low for FEF25%-75% at any age.