Multilevel multiple imputation
For the main outcome variables of the sum of DDD of PPI, there were 0.7% missing values at time T0, 2.8% missing values at time T1, and 10.8% missing values at time T2, with these occurring exclusively in the intervention group at time T0 and similar distribution between the two groups at the other time points. Multilevel multiple imputation was performed using the R package mice 3.11.0 and method 2l.norm, which uses the linear mixed model with heterogeneous error variance