Characteristics of the total population and children with and without asthma ever at age 6 years.

Values are absolute numbers (percentages) for categorical variables. Gestational age at birth and birth weight are reported in means (standard deviation), and the median (range) was reported for FeNO and Rint.
*Asthma data may not add up to 6717 because of missing data (n = 1764, 26.6%). Information on physician-diagnosed asthma ever (yes, no) was obtained at age 6 years. 7% (328/4953) of the children had a diagnosis of asthma.
+Chi-squared test.
aPercentage of missing data of total study population (N = 6717): teenage pregnancy (0%), parity (4%), smoking during pregnancy (19%), single parenting (9%), parental education (6%), net household income (18%), financial difficulties (26%), paternal unemployment (23%), maternal unemployment (18%), maternal psychopathology (26%), maternal BMI (10%), maternal history of asthma or atopy (19%), child's male sex (0%), child's ethnicity (2%), gestational age at birth (0%), birth weight (0%), breastfeeding ever (22%), tobacco smoke exposure (38%), pet exposure at home (32%), daycare attendance (32%), eczema ever (27%), respiratory tract infections (17%), wheezing 24%), FeNO (41%) and Rint (34%).