Percent of people with cystic fibrosis by age with normal/mild forced expiratory volume in one second (FEV
), moderate FEV
and severe FEV
. The majority of children have FEV1 values in the normal to mild range, indicating mild disease and mild airway obstruction. Adults age 18–29 and 30+ have FEV1 values in the moderate to severe range, indicating severe disease and increased airway obstruction (downloaded from Cystic Fibrosis Foundation website at http://www.cff.org/UploadedFiles/Research/ClinicalResearch/2011-Patient-Registry.pdf).