Table 1.

Exclusion and censoring criteria

Medical condition	International classification of disease, 9th modification ICD-9 diagnosis code
Emphysema	492.x
Chronic obstructive pulmonary disease including chronic bronchitis	490.x–491.x
Bronchiectasis	494.x
Chronic airway obstruction	496.x
Chronic respiratory conditions due to fumes and vapors	506.4
Cystic fibrosis	277.0
Prior history of asthma	493.x