= Solution
A <group sequential design> can stop early when the treatment is insufficiently promising, reducing expected recruitment, patient exposure and cost when the effect is poor. It also allows a planned decision before maximum enrollment.
A disadvantage is that the analysis is selected by the interim results: <estimation> and uncertainty must account for stopping, and power and operational planning depend on the stopping rule. The following parts quantify the resulting conditional <estimation> bias. If a design also allows repeated efficacy tests, its rejection boundaries must control overall <Type I error>. In the present futility-only design, stopping without rejection need not inflate the error rate of a single prespecified final test; it can make that test conservative. \b[Earlier decisions are valuable, but the ordinary fixed-sample analysis is not automatically appropriate after selection.]
Back to article page
