Statistical analysis
Comparisons between the constipation group and non-constipation group
were using absolute standardized differences (ASD). Whenever the ASD
were less than 0.1, the characteristics of the two groups were deemed to
be similar. On the other hand, Kaplan-Meier analysis was applied to
calculate the cumulative incidence of asthma and then log-rank test was
used to test the significance. Cox proportional hazard model was applied
to estimate the hazard ratio of asthma between the constipation and
non-constipation groups.