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Blinded and unblinded sample size reestimation procedures for stepped-wedge cluster randomized trials

Lookup NU author(s): Dr Michael GraylingORCiD, Professor James WasonORCiD



This work is licensed under a Creative Commons Attribution 4.0 International License (CC BY 4.0).


© 2018 The Authors. Biometrical Journal Published by WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. The ability to accurately estimate the sample size required by a stepped-wedge (SW) cluster randomized trial (CRT) routinely depends upon the specification of several nuisance parameters. If these parameters are misspecified, the trial could be overpowered, leading to increased cost, or underpowered, enhancing the likelihood of a false negative. We address this issue here for cross-sectional SW-CRTs, analyzed with a particular linear-mixed model, by proposing methods for blinded and unblinded sample size reestimation (SSRE). First, blinded estimators for the variance parameters of a SW-CRT analyzed using the Hussey and Hughes model are derived. Following this, procedures for blinded and unblinded SSRE after any time period in a SW-CRT are detailed. The performance of these procedures is then examined and contrasted using two example trial design scenarios. We find that if the two key variance parameters were underspecified by 50%, the SSRE procedures were able to increase power over the conventional SW-CRT design by up to 41%, resulting in an empirical power above the desired level. Thus, though there are practical issues to consider, the performance of the procedures means researchers should consider incorporating SSRE in to future SW-CRTs.

Publication metadata

Author(s): Grayling MJ, Mander AP, Wason JMS

Publication type: Article

Publication status: Published

Journal: Biometrical Journal

Year: 2018

Volume: 60

Issue: 5

Pages: 903-916

Print publication date: 01/09/2018

Online publication date: 03/08/2018

Acceptance date: 27/06/2018

Date deposited: 08/03/2019

ISSN (print): 0323-3847

ISSN (electronic): 1521-4036

Publisher: Wiley-VCH Verlag


DOI: 10.1002/bimj.201700125


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