The hunt for efficient, incomplete designs for stepped wedge trials with continuous recruitment and continuous outcome m
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(2020) 20:279
RESEARCH ARTICLE
Open Access
The hunt for efficient, incomplete designs for stepped wedge trials with continuous recruitment and continuous outcome measures Richard Hooper1,2* , Jessica Kasza3 and Andrew Forbes3
Abstract Background: We consider the design of stepped wedge trials with continuous recruitment and continuous outcome measures. Suppose we recruit from a fixed number of clusters where eligible participants present continuously, and suppose we have fine control over when each cluster crosses to the intervention. Suppose also that we want to minimise the number of participants, leading us to consider “incomplete” designs (i.e. without full recruitment). How can we schedule recruitment and cross-over at different clusters to recruit efficiently while achieving good precision? Methods: The large number of possible designs can make exhaustive searches impractical. Instead we consider an algorithm using iterative improvements to hunt for an efficient design. At each iteration (starting from a complete design) a single participant – the one with the smallest impact on precision – is removed, and small changes preserving total sample size are made until no further improvement in precision can be found. Results: Striking patterns emerge. Solutions typically focus recruitment and cross-over on the leading diagonal of the cluster-by-time diagram, but in some scenarios clusters form distinct phases resembling before-and-after designs. Conclusions: There is much to be learned about optimal design for incomplete stepped wedge trials. Algorithmic searches could offer a practical approach to trial design in complex settings generally. Keywords: Algorithms, Cluster randomised trials, Continuous recruitment, Efficient design, Stepped wedge trials
Background Stepped wedge trials are cluster-randomised trials where clusters cross over from the control to the active intervention condition during the trial, according to a randomised schedule [1]. Typically, every cluster will begin the trial in the control condition and end in the intervention condition, but the stepped wedge design in the broadest sense * Correspondence: [email protected] 1 Queen Mary University of London, London, UK 2 Institute of Population Health Sciences, Yvonne Carter Building, 58 Turner Street, Whitechapel, London E1 2AB, UK Full list of author information is available at the end of the article
allows for more variation than this, including the possibility that some clusters remain in the same condition throughout [2]. The classic schematic representation of a stepped wedge trial shows time separated into regular or discrete “periods” [2], though the reality is that many stepped wedge trials recruit participants continuously over the duration of the trial [3]. Few authors have considered possibilities for the design of stepped wedge trials where cross-over can be scheduled on a continuous time-scale [4]. Another common assumption is that recruitment to a stepped wedge trial occurs in every period in every
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