Group sequential designs are used to facilitate the conduct of interim analyses.

• A. No
• B. They replace the need for a control group
• C. Yes
• D. Only at the end

Answer: (C)

Group sequential designs are structured so that the trial data are examined at predefined interim points rather than waiting until the end. This setup lets researchers assess early results to decide whether the study should continue, stop early for a clear treatment benefit, stop for futility, or pause for safety concerns, all while keeping the overall chance of a false positive under control through planned statistical boundaries.

This approach speeds up answering the research question and can reduce exposure of participants to an inferior or non-beneficial treatment, but it does not replace having a control group. A comparator is still needed to interpret effects, and the design simply governs when and how interim looks occur and how the decision rules are applied. Interim analyses are a key feature, not something reserved only for the final analysis.