Statistical analysis
In the main model, a 2-level logistic regression was employed to
estimate associations of different family history types with childhood
asthma. Children were considered as the first level and studied
districts were the second level. The reference group was participants
who had no family member affected asthma. Odds ratios (ORs) and its 95%
confidence intervals (CIs) were calculated after adjusting for
covariates. Mediation effects of parents between grandparental asthma
and childhood asthma were estimated using R package mediation and
95%CIs were estimated using quasi-Bayesian approximation (100
simulations). All statistical tests were two-tailed. P<0.05 was considered statistically significant in the study.
Data analyses were conducted using R version 3.6.3. The computation was
fulfilled in the high-performance computer system in the School of
Public Health, Sun Yat-sen University.