# Confidence Intervals for Adaptive Trial Designs II: Case Study and Practical Guidance

## TL;DR

This paper provides practical guidance on choosing and reporting confidence intervals in adaptive clinical trials to avoid misleading results.

## Contribution

The paper proposes specific guidelines for selecting and reporting confidence intervals in adaptive trial designs.

## Key findings

- Confidence intervals in adaptive trials can have notably different statistical properties.
- A comprehensive simulation study highlights the variability in performance of different CI methods.
- Guidelines are proposed to help researchers choose and report CIs effectively in adaptive designs.

## Abstract

In adaptive clinical trials, the conventional confidence interval (CI) for a treatment effect is prone to undesirable properties such as undercoverage and potential inconsistency with the final hypothesis testing decision. Accordingly, as is stated in recent regulatory guidance on adaptive designs, there is the need for caution in the interpretation of CIs constructed during and after an adaptive clinical trial. However, it may be unclear which of the available CIs in the literature are preferable. This paper is the second in a two‐part series that explores CIs for adaptive trials. Part I provided a methodological review of approaches to construct CIs for adaptive designs. In this paper (Part II), we present an extended case study based around a two‐stage group sequential trial, including a comprehensive simulation study of the proposed CIs for this setting. This facilitates an expanded description of considerations around what makes for an effective CI procedure following an adaptive trial. We show that the CIs can have notably different properties. Finally, we propose a set of guidelines for researchers around the choice of CIs and the reporting of CIs following an adaptive design.