Statistics
The prevalence of wheeze/asthma was calculated as the ratio of cases to
total number of responders. The Mantel-Haenzel extension of chi-square
test for trends was applied to evaluate prevalence tendency among
surveys. Prevalence rate ratios (i.e. prevalence rate changes) between
consecutive surveys were calculated by logistic regression analysis with
adjustment for sex. Spirometric parameters were compared with one-way
ANOVA with Tukey’s post-hoc test for multiple comparisons. Statistical
analyses were performed in IBM SPSS version 25 (IBM Corp., Armonk, NY).