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Developing guidance for a risk-proportionate approach to blinding statisticians within clinical trials: a mixed methods study

Iflaifel, Mais; Sprange, Kirsty; Bell, Jennifer; Cook, Andrew; Gamble, Carrol; Julious, Steven A.; Juszczak, Edmund; Linsell, Louise; Montgomery, Alan; Partlett, Christopher

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Mais Iflaifel

Jennifer Bell

Andrew Cook

Carrol Gamble

Steven A. Julious

Louise Linsell

Director Nottingham Clinical Trials Unit

Assistant Professor of Medical Statistics and Clinical Trials


Background: Existing guidelines recommend statisticians remain blinded to treatment allocation prior to the final analysis and that any interim analyses should be conducted by a separate team from the one undertaking the final analysis. However, there remains substantial variation in practice between UK Clinical Trials Units (CTUs) when it comes to blinding statisticians. Therefore, the aim of this study was to develop guidance to advise CTUs on a risk-proportionate approach to blinding statisticians within clinical trials. Methods: This study employed a mixed methods approach involving three stages: (I) a quantitative study using a cohort of 200 studies (from a major UK funder published between 2016 and 2020) to assess the impact of blinding statisticians on the proportion of trials reporting a statistically significant finding for the primary outcome(s); (II) a qualitative study using focus groups to determine the perspectives of key stakeholders on the practice of blinding trial statisticians; and (III) combining the results of stages I and II, along with a stakeholder meeting, to develop guidance for UK CTUs. Results: After screening abstracts, 179 trials were included for review. The results of the primary analysis showed no evidence that involvement of an unblinded trial statistician was associated with the likelihood of statistically significant findings being reported, odds ratio (OR) 1.02 (95% confidence interval (CI) 0.49 to 2.13). Six focus groups were conducted, with 37 participants. The triangulation between stages I and II resulted in developing 40 provisional statements. These were rated independently by the stakeholder group prior to the meeting. Ten statements reached agreement with no agreement on 30 statements. At the meeting, various factors were identified that could influence the decision of blinding the statistician, including timing, study design, types of intervention and practicalities. Guidance including 21 recommendations/considerations was developed alongside a Risk Assessment Tool to provide CTUs with a framework for assessing the risks associated with blinding/not blinding statisticians and for identifying appropriate mitigation strategies. Conclusions: This is the first study to develop a guidance document to enhance the understanding of blinding statisticians and to provide a framework for the decision-making process. The key finding was that the decision to blind statisticians should be based on the benefits and risks associated with a particular trial.


Iflaifel, M., Sprange, K., Bell, J., Cook, A., Gamble, C., Julious, S. A., …Partlett, C. (2023). Developing guidance for a risk-proportionate approach to blinding statisticians within clinical trials: a mixed methods study. Trials, 24, Article 71.

Journal Article Type Article
Acceptance Date Dec 7, 2022
Online Publication Date Jan 31, 2023
Publication Date Jan 31, 2023
Deposit Date Jan 18, 2023
Publicly Available Date Jan 31, 2023
Electronic ISSN 1745-6215
Peer Reviewed Peer Reviewed
Volume 24
Article Number 71
Public URL
Publisher URL


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