Verifying the Precision of Effect Size Estimators from Cluster Randomised and Multisite Trials: A Simulation Study Using the Educational Platform Trial Simulator, epts

To assess the effectiveness of educational interventions, randomised controlled trials are typically run across multiple schools. Multilevel models are fitted to account for pupil nesting within schools and the trial design – mostly cluster randomised or multisite trials – from which effect size estimates are obtained. However, several conventions exist for estimating effect sizes (total/within and unconditional/conditional) as well as for model fitting (ANCOVA-type or longitudinal models, standardised or non-standardised outcomes). This research examines the sensitivity, precision and robustness of effect size estimates to these choices.We conduct a simulation study using the R package epts, an educational trial simulator that generates synthetic datasets for randomised controlled trials using customised parameters. The simulation settings are motivated by design parameters corresponding to published Education Endowment Foundation reports. This approach aims to identify optimal trial design characteristics that improve the precision and magnitude of estimated effect sizes for an educational outcome such as pupil attainment. The findings are expected to provide practical reference for the design of future educational trials.