Flow of subject recruitment, retention, and integration the Asthma Rhinitis Cohort and Severe Asthma Cohort. Of the 549 subjects in the Merged Asthma Cohort, 189 (35%) were originally recruited from pulmonary and allergy specialty practices, 38 (7%) from family medicine practices, 88 (16%) by random digit dial, and 234 (42%) based on prior hospitalization for asthma.