Statistical Analyses
Data were analyzed using a modified Poisson regression approach that
allowed for estimation of risk ratios instead of odds ratios24. Models were adjusted for child’s sex, maternal
education level (<high school, high school, >high
school), mother’s age, average PM2.5 during pregnancy,
and average PM2.5 during the first year postpartum. We
then examined effect modification by child sex (male/female) for
respiratory outcomes by including the relevant interaction terms. Models
with p-values <0.1 for interaction terms were then stratified
by child sex. In sensitivity analysis, we also adjusted for average
PM2.5 during the first two years postpartum,
breastfeeding, and for SES instead of maternal education. Analyses were
performed in R Version 3.5.1 (R Development Core Team) and SPSS version
24 (Chicago, IL).