Protocol for the Delphi study on checklist for the reporting of sample size in trial grant application and protocols for adaptive design

This Delphi study is designed to achieve expert consensus on key items that should be reported when describing sample size determination in adaptive clinical trial protocols and grant applications. It is a core component of the AD-DELTA2 project, which aims to develop a dedicated reporting guideline to improve transparency, reproducibility, and completeness in this area.

The study will build on findings from earlier phases of the project, including a systematic review of adaptive design protocols and funding documents, and qualitative interviews with key stakeholders. Based on this preliminary work, a draft list of candidate reporting items has been developed.

A two-round, online Delphi process will be conducted. In Round 1, participants will be asked to rate the importance of each item using a 9-point Likert scale and provide optional qualitative feedback. Items will be retained, revised, or dropped based on predefined consensus thresholds. In Round 2, participants will re-rate the remaining items, informed by a summary of the group’s Round 1 responses.

Participants will be purposively selected to ensure a range of perspectives, including trialists, statisticians, funders, regulators, and patient/public contributors. A final consensus meeting will follow the Delphi rounds to discuss unresolved items, clarify terminology, and finalise the checklist content.

The outcome of this study will be a consensus-based checklist to guide reporting of sample size considerations in adaptive trial protocols and funding submissions.

This project has received ethical approval from the Ethics Committee of the School of Medicine and Population Health, University of Sheffield (Reference No. 210127508).