Review Finds Poor Reporting of Bayesian Borrowing in Phase II Trials

A scoping review of Phase II clinical trials has identified poor reporting across multiple aspects of Bayesian robust information borrowing, highlighting a gap between methodological developments and practical uptake in trial design. Out of 1,282 articles retrieved through literature searches, 37 studies were included in the evaluation. The review revealed that fixed downweighting was the most commonly used borrowing method, with only slightly more than a third of the studies providing details on its implementation.

Incorporating external information into clinical study designs has received increasing attention in recent years, as efficiency gains and sample size reductions can be achieved when external data are consistent with current trial data. This efficiency makes borrowing attractive when patient recruitment is difficult. However, unexpected inconsistency cannot be ruled out, leading to the development of robust borrowing approaches such as the power prior, meta-analytic predictive prior, robust mixture prior, and Bayesian hierarchical model to limit potential losses, though their use in actual trials remains underexplored.

To investigate the use of external information in Phase II clinical trials, the researchers searched PubMed Central and the Cochrane Central Register of Controlled Trials, alongside citation searches in key methodological papers. The authors assessed whether and how the suitability of external data was evaluated, the borrowing methods utilized, and the specification and justification of tuning parameters that influence the degree of borrowing. Overall, the researchers found poor reporting across these aspects, signaling a persistent gap between methodological developments and the practical uptake and reporting of Bayesian borrowing methods.

Subject of Research: Bayesian robust information borrowing in Phase II clinical trials

Article Title: Uptake of Bayesian robust information borrowing in Phase II clinical trials: a scoping review

Article References: Weru, V., Calderazzo, S., Held, L., Wiesenfarth, M., & Kopp-Schneider, A. (2026). Uptake of Bayesian robust information borrowing in Phase II clinical trials: a scoping review. BMC Medical Research Methodology. https://doi.org/10.1186/s12874-026-03052-3

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DOI: 10.1186/s12874-026-03052-3

Keywords: Bayesian borrowing, Phase II clinical trials, scoping review, fixed downweighting, power prior, robust mixture prior, Bayesian hierarchical model, clinical study design, Uptake, Bayesian, robust, information