Abstract
BackgroundControlled implementation trials often randomize the intervention at the site level, enrolling relatively few sites (e.g., 6–20) compared to trials that randomize by subject. Trials with few sites carry a substantial risk of an imbalance between intervened (cases) and non-intervened (control) sites in important site characteristics, thereby threatening the internal validity of the primary comparison. A stepped wedge design (SWD) staggers the intervention at sites over a sequence of times or time waves until all sites eventually receive the intervention. We propose a new randomization method, sequential balance, to control time trend in site allocation by minimizing sequential imbalance across multiple characteristics. We illustrate the new method by applying it to a SWD implementation trial.MethodsThe trial investigated the impact of blended internal-external facilitation on the establishment of evidence-based teams in general mental health clinics in nine US Department of Veterans Affairs medical centers. Prior to randomization to start time, an expert panel of implementation researchers and health system program leaders identified by consensus a series of eight facility-level characteristics judged relevant to the success of implementation. We characterized each of the nine sites according to these consensus features. Using a weighted sum of these characteristics, we calculated imbalance scores for each of 1680 possible site assignments to identify the most sequentially balanced assignment schemes.ResultsFrom 1680 possible site assignments, we identified 34 assignments with minimal imbalance scores, and then randomly selected one assignment by which to randomize start time. Initially, the mean imbalance score was 3.10, but restricted to the 34 assignments, it declined to 0.99.ConclusionsSequential balancing of site characteristics across groups of sites in the time waves of a SWD strengthens the internal validity of study conclusions by minimizing potential confounding.Trial registrationRegistered at ClinicalTrials.gov as clinical trials # NCT02543840; entered 9/4/2015.
Highlights
Controlled implementation trials often randomize the intervention at the site level, enrolling relatively few sites (e.g., 6–20) compared to trials that randomize by subject
We propose first finding a subset of site assignments that have low mean-imbalance scores and searching over the subset for site assignments that have low imbalance scores
In calculating the imbalance score for our stepped wedge design (SWD) trial, the primary set of factor representations used equal weights and re-expressed all continuous characteristics as categorical variables using the tertiles of the continuous variables to define the categories, as summarized above
Summary
Controlled implementation trials often randomize the intervention at the site level, enrolling relatively few sites (e.g., 6–20) compared to trials that randomize by subject. We propose a new randomization method, sequential balance, to control time trend in site allocation by minimizing sequential imbalance across multiple characteristics. Balancing comparison groups is a longstanding challenge for both controlled trials and observational studies. Subject-level randomization designs draw from a Stratified randomization is impractical when the site profile contains multiple relevant healthcare site characteristics, each of which would ideally be balanced across study conditions. Lew et al Implementation Science (2019) 14:46 socio-economically similar populations. The research team would need to decide whether stratifying based on region or socio-economic status would better serve the study goals
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