Statistical Analyses
We analysed asthma, FENO, allergen-specific IgE level,
and eosinophils, in a four-variate twin model. In this model, the
covariance between variables within individuals, as well as the
covariance between twins in pairs, are explicitly modelled in structural
equation models. Asthma was analyzed as a binary variable and adjusted
for age and sex. The data for FENO, allergen-specific
IgE level, and eosinophils were all log-transformed to obtain a
distribution closer to normal, and adjustments were done for ICS, age
and sex. Due to the sampling scheme, the population may have a skewed
distribution (compared to the source population) of investigated
variables; thus, we re-weighted all analyses according to sampling
probability.