A unifying family of group sequential test designs

Currently, the design of group sequential clinical trials requires choosing among several distinct design categories, design scales, and strategies fo r determining stopping rules. This approach can limit the design selection process so that clinical issues are not fully addressed. This paper describ es a family of designs that unifies previous approaches and allows continuo us movement among the previous categories. This unified approach facilitate s the process of tailoring the design to address important clinical issues. The unified family of designs is constructed from a generalization of a fo ur-boundary group sequential design in which the shape and location of each boundary can bt: independently specified. Methods for implementing the des ign using error-spending functions are described. Examples illustrating the use of the design family are also presented.