Statistical analysis
The data were analyzed using SPSS version 21.0 (SPSS, Chicago, IL) and R software version 3.6.3. Continuous data are expressed as means with standard deviations or as medians with the interquartile ranges, depending on the data distribution. The relationships of the concentrations of different of urinary phthalates with serum periostin level, Rrs5, and Rrs5-20 were analyzed using linear regression with adjustment for height, gender, BMI z -score, aeroallergen sensitization, secondary smoking, and vitamin D level. The estimates were regression slopes for phthalate concentration vs. periostin level and Rrs5. Beta (β) and a 95% confidence interval (CI) were obtained from a generalized linear regression model with the gamma function. The R package, “Mediation”19 was used to quantitatively estimate the mediating effect of periostin level in the association of phthalate concentration with Rrs5 and Rrs5-20. This package estimates confidence intervals using bootstrapping with 1000 resamples. A two-sided P value of .05 or less indicated statistical significance.