MRT-SS Calculator: An R Shiny Application for Sample Size Calculation in Micro-Randomized Trials

Abstract: The micro-randomized trial (MRT) is a new experimental design which allows for the investigation of the proximal effects of a "just-in-time" treatment, often provided via a mobile device as part of a mobile health intervention. As with a traditional randomized controlled trial, computing the minimum required sample size to achieve a desired power is a crucial step in designing an MRT. We present MRT-SS Calculator, an online sample-size calculator for micro-randomized trials, built with R Shiny. MRT-SS Calculator requires specification of time-varying patterns for the proximal treatment effect and expected treatment availability. We illustrate the implementation of MRT-SS Calculator using a mobile health trial, HeartSteps. The application can be accessed from https://pengliao.shinyapps.io/mrt-calculator.