Self-reported common cold incidence and duration are compared for different occupancy levels in Figure 1 . With incrementally increasing occupancy in dorm rooms, the proportion of occupants with $6 common colds increased significantly (p = 0.002), as did the proportion of occupants with $2 weeks common cold duration (p = 0.000). The odds ratios of crowdedness for common cold incidence of $6 times and duration of $2 weeks, adjusted for gender, age, hours spent indoors, family members' asthma and allergy history, environmental tobacco smoke exposure are shown in Figure 2 . Students in 6-person rooms were about 2.0 times as likely to have a common cold incidence $6 times per year and a duration $2 weeks, as students in 3-person dorm rooms.