Post-albuterol forced expiratory volume in 1 second (FEV1) and forced vital capacity (FVC) will be performed using calibrated spirometers in accordance with guidelines established by the American Thoracic Society. A uniform set of nomograms (NHANES III) will be used at all sites. The best of three efforts will be defined as the highest FEV1 and the highest FVC obtained on any of the three blows (even if not from the same curve with a maximum of 5 attempts).