Study design and intervention
Trials-Equity
This study is based on a cluster-randomized controlled trial comparing a multicomponent ECD intervention, ‘Learning Clubs’, with the usual standard of maternal and child healthcare in rural Vietnam (As outlined in previous studies, the primary outcome was child cognitive development composite score at 2 years of age assessed by the Bayley Scale of Infant and Toddler Development Third Edition (Bayley-III). The number of clusters and sample size were determined to detect a difference in the proportion of children scoring <1 SD on the Bayley-III of 15% in the control arm and 8% in the intervention arm (with 80% statistical power and a significance level of 0.05; intracluster correlation coefficient = 0.03) (This study followed Consolidated Standards of Reporting Trials-Equity guidelines 2017 (