The R package rpact has been developed to design sequential and adaptive experiments. Many of the functions of the R package are available in an online Shiny app. For more information about rpact, including a quick start guide and manual, visit the rpact website. This step by step vignette accompanies the manuscript “Group Sequential Designs: A Tutorial” by Lakens, Pahlke, & Wassmer (2021).
The online shiny app for rpact is available at https://shiny.rpact.com. The default settings when the Shiny app is loaded is for a fixed sample design, which means that there is only one look at the data (kMax = 1). In other words, the default setting is not for a sequential design, but a traditional design where the data is analyzed once. Moving the slider for the “Maximum number of stages” would increase the number of looks in the design (you can select up to up to 10 looks).