Stopping rules for clinical trials incorporating clinical opinion.

A method is described of eliciting a 'range of equivalence', i.e. a range of differences between two treatments over which a group of clinical trial participants would have no clear preference for either treatment. This range of equivalence is then incorporated into a formal stopping rule for the trial using an extension of the group sequential design. Tables for the implementation of the design are presented. The method is discussed in the context of other sequential-trial designs.