Table 1– Characteristics of study population and comparisons of exhaled nitric oxide fraction (FeNO) levels
VariableSubjects#FeNOp-value+
Sex
 Girls1146 (51.16)11.02±6.610.53
 Boys1094 (48.84)11.25±7.08
Age yrs
 <8703 (31.38)10.8±6.590.005
 8–91102 (49.20)11.02±6.5
 >9435 (19.42)12.18±8.28
Race/ethnicity
 Non-Hispanic White828 (37.01)10.28±5.96<0.0001
 Hispanic1247 (55.74)11.59±7.07
 African–American61 (2.73)11.82±8.28
 Asian86 (3.84)14.15±11.04
 Other15 (0.67)10.8±3.89
Asthma
 Yes169 (7.54)13.87±10.41<0.0001
 No2071 (92.46)10.91±6.55
History of respiratory allergy
 Yes1167 (52.10)11.94±8<0.0001
 No1073 (47.90)10.38±5.61
Questionnaire language
 Spanish531 (23.71)12.3±7.51<0.0001
 English1709 (76.29)10.8±6.59
Body mass index
 Underweight <5th percentile49 (2.19)10.8±5.620.85
 Normal 5th to <85th percentile1368 (61.29)11.25±6.97
 Overweight 85th to <95th percentile395 (17.70)11.13±7.13
 Obese >95th percentile420 (18.82)10.91±6.44
FeNO collected outside classroom
 Yes111 (4.96)14.88±9.82<0.0001
 No2129 (95.04)11.02±6.72
Parental education
 Less than high school424 (20.06)12.55±7.78<0.0001
 High school390 (18.45)11.13±7.24
 Above high school1300 (61.49)10.8±6.48
Exposure to second-hand smoke
 Yes102 (4.55)12.06±7.840.20
 No2123 (94.78)11.13±6.79
In utero exposure to maternal smoking
 Yes130 (6.11)10.28±6.060.11
 No1998 (93.89)11.25±6.97
  • Data are presented as n (%) or mean±sd, unless otherwise stated. #: numbers do not always add up because of missing data; : geometric mean and sd obtained from a univariate model testing equality of group means; +: tests for the equality of group means (did not include missing category).