Optimising the design of internal pilot work to inform efficient randomised controlled trials: issues to consider when developing progression criteria

Background An internal pilot study is the first part of a substantive RCT where trial parameters are examined and data contribute to the final analyses. This two-phase design provides an opportunity to review pre-agreed ‘progression criteria’ that determine whether the internal pilot should continue into the main trial. Selecting appropriate criteria is critical but little is known about this area. Key issues in selecting progression criteria when designing RCTs with an internal pilot phase are considered.