Analysis
We followed the similar methods as the cost-effectiveness study of the ‘Learning Clubs’ cluster-randomized trial (Multiple imputations were used to handle missing data on out-of-pocket healthcare costs based on the log multiple imputation predictive mean matching algorithm as reported in the cost-effectiveness study (The incremental cost-effectiveness ratios (ICERs) were estimated by dividing the mean difference in costs by the mean difference in effects for each subgroup based on household wealth and mother’s education level. In addition to estimating ICERs based on intervention cost and out-of-pocket healthcare cost adjusting for cluster effects and baseline characteristics, we also estimated ICERs under different scenarios that include intervention cost alone without out-of-pocket healthcare costs or results adjusting for cluster effects. We used non-parametric cluster bootstrapping by randomly resampling clusters with replacement and presented mean and 95% CI of ICERs from 1000 bootstrap replications by subgroups. The bootstrap estimates were plotted on the cost-effectiveness plane and used to estimate the probability that the intervention was cost-saving or cost-effective. Since there was no national cost-effectiveness threshold per child cognitive score gained, we used alternative threshold of US$56, which is 2% of Vietnam’s gross domestic product (GDP) (All analyses used the SAS 9.4 software and Microsoft Excel Office 2019.