Acknowledgements
Thanks to John Lueders for co-authoring the first version of the Shiny app documented here and in the initial draft of this book. John showed me (Keaven) the importance of a great interface designer and collaborator. Thanks also to Joy Ge for review and comments on the text to make the presentation more clear. Thanks to Judy Anderson for allowing Keaven to spend time working to enable group sequential designs with the gsDesign package and its associated interface. Many people have helped make gsDesign a better package in many ways; see its contributors page on GitHub. We also thank Merck & Co., Inc., Rahway, NJ, USA for allowing us time and outside resources to work on gsDesign and its Shiny interface. Thanks to many colleagues inside and outside Merck & Co., Inc., Rahway, NJ, USA who have used the package and to those who have taken time to submit issues or pull requests to our GitHub repository. Our purpose is to enable all of you.
Thanks to Dr. Eva Hiripi from Springer for encouraging publication of this work and to Springer for allowing us to support an online version of this work at https://keaven.github.io/gsd-shiny/.