Statistical analysis
Comparisons between the constipation group and non-constipation group were demonstrated by using absolute standardized differences (ASD). When the absolute standardized differences were less than 0.1, the characteristics of the two groups were deemed to be similar.21 Kaplan-Meier analysis was performed to evaluate the cumulative incidence of atopic dermatitis and log-rank test was utilized to test the significance. Cox proportional hazard model was applied to estimate the hazard ratio of atopic dermatitis between the constipation group and non-constipation group. Analyses were performed using statistical software SPSS version 18.0.