O’Brien-Fleming and Pocock stopping boundaries for interim analyses
This calculator computes group sequential stopping boundaries for planned interim analyses, using Lan-DeMets alpha-spending functions (O’Brien-Fleming-type or Pocock-type) with equally-spaced information fractions, found via recursive numerical integration of the sequential test statistics’ joint distribution. Simulation during development confirmed the boundaries control the overall two-sided Type I error very closely to the specified α, within the tolerance of the numerical-grid integration used to find them.