Daniel J Bratton | Searcharxiv

arXiv2026

Assessing the Impact of Intercurrent Events on Power and Sample Size for Estimands with Time-to-Event Endpoints

The precise definition of a primary estimand, accounting for intercurrent events (IEs) as per the ICH E9(R1) addendum, is fundamental to the design and interpretation of clinical trials. Conventional power and sample size calculations, however, often do not adequately incorporate the impact of IEs and their corresponding handling strategies, creating a risk of over- or under-powered studies. While simulation-based approaches can address this complexity, they are often computationally intensive and may only explore a limited set of scenarios. In this paper, we introduce a set of formulae for calculating power for estimands with time-to-event endpoints, applied to trials with fixed follow-up durations. We focus on estimands that use treatment policy, hypothetical, composite, or a combination of strategies for handling IEs, under the assumption that IEs occur independently of each other and the primary endpoint. Validation against simulation-based estimates shows strong agreement, and we explore deviations in power estimates in scenarios where outcomes and IEs are dependent. We illustrate the practical application of our approach through a case study in nasal polyposis, examining the sensitivity of sample size requirements to varying IE rates and their impacts on post-IE outcomes. The proposed formulae facilitate rapid and accurate power and assurance calculations, enabling clinical trial designs to be more closely aligned with the estimand of interest.

stat.ME↗

arXiv2019

Adding new experimental arms to randomised clinical trials: impact on error rates

Background: Experimental treatments pass through various stages of development. If a treatment passes through early phase experiments, the investigators may want to assess it in a late phase randomised controlled trial. An efficient way to do this is adding it as a new research arm to an ongoing trial. This allows to add the new treatment while the existing arms continue. The familywise type I error rate (FWER) is often a key quantity of interest in any multi-arm trial. We set out to clarify how it should be calculated when new arms are added to a trial some time after it has started. Methods: We show how the FWER, any-pair and all-pairs powers can be calculated when a new arm is added to a platform trial. We extend the Dunnett probability and derive analytical formulae for the correlation between the test statistics of the existing pairwise comparison and that of the newly added arm. We also verify our analytical derivation via simulations. Results: Our results indicate that the FWER depends on the shared control arm information (i.e. individuals in continuous and binary outcomes and primary outcome events in time-to-event outcomes) from the common control arm patients and the allocation ratio. The FWER is driven more by the number of pairwise comparisons and the corresponding (pairwise) Type I error rates than by the timing of the addition of the new arms. The FWER can be estimated using Šidák's correction if the correlation between the test statistics of pairwise comparisons is less than 0:30. Conclusions: The findings we present in this article can be used to design trials with pre-planned deferred arms or to design new pairwise comparisons within an ongoing platform trial where control of the pairwise error rate (PWER) or FWER (for a subset of pairwise comparisons) is required.

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