Adaptive Solomon Four-Group Design — Pretest Control with Sequential Allocation

The Adaptive Solomon Four-Group Design combines the pretest-sensitization control of Solomon's classic four-group structure with response-adaptive randomization, allowing interim outcome data to update the allocation probabilities across the four groups as the study progresses. This hybrid preserves the design's ability to isolate the testing effect while improving ethical efficiency by steering more participants toward conditions performing better at interim checkpoints.