A method to reduce imbalance for site-level randomized stepped wedge implementation trial designs
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METHODOLOGY
Open Access
A method to reduce imbalance for site-level randomized stepped wedge implementation trial designs Robert A. Lew1,2, Christopher J. Miller1,2, Bo Kim1,2, Hongsheng Wu4, Kelly Stolzmann1 and Mark S. Bauer1,3*
Abstract Background: 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. 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. Methods: The 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. Results: From 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. Conclusions: Sequential 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 registration: Registered at ClinicalTrials.gov as clinical trials # NCT02543840; entered 9/4/2015. Keywords: Stepped wedge, Imbalance, Nested control trails
Background Balancing comparison groups is a longstanding challenge for both controlled trials and observational studies. The issue is particularly acute in designs that randomize by site. Typically, subject-level randomization designs draw from a
* Correspondence: [email protected] 1 VA Boston Healthcare System, Center for Healthcare Organization and Implementation Research, 150 South Huntington Avenue, Jamaica Plain, Boston, MA 02130, USA 3 Department of Psychiatry, Harvard Medical School, Boston, MA, USA Full list of author information is available at the end of the article
large pool, while site-level randomization draws f
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