Fig 1.

Common types of adaptive trials. Sample size reassessment: if interim analysis shows worse results than expected, the sample size can be reassessed and increased to ensure that the trial is adequately powered. Response adaptive randomisation: if interim analysis shows promising results for a treatment, the allocation ratio can be modified to favours enrolment to that treatment. Adaptive enrichment: if interim analysis shows that a treatment has more promising results in one subgroup of patients, the study eligibility criteria can be modified to investigate the efficacy of the intervention in the that subgroup, with a sample size reassessment to ensure a sufficient sample size. SSR=sample size reassessment