Designing a stepped wedge trial: three main designs, carry-over effects and randomisation approaches
Open Access
- 17 August 2015
- journal article
- research article
- Published by Springer Science and Business Media LLC in Trials
- Vol. 16 (1), 1-12
- https://doi.org/10.1186/s13063-015-0842-7
Abstract
There is limited guidance on the design of stepped wedge cluster randomised trials. Current methodological literature focuses mainly on trials with cross-sectional data collection at discrete times, yet many recent stepped wedge trials do not follow this design. In this article, we present a typology to characterise the full range of stepped wedge designs, and offer guidance on several other design aspects. We developed a framework to define and report the key characteristics of a stepped wedge trial, including cluster allocation and individual participation. We also considered the relative strengths and weaknesses of trials according to this framework. We classified recently published stepped wedge trials using this framework and identified illustrative case studies. We identified key design choices and developed guidance for each. We identified three main stepped wedge designs: those with a closed cohort, an open cohort, and a continuous recruitment short exposure design. In the first two designs, many individuals experience both control and intervention conditions. In the final design, individuals are recruited in continuous time as they become eligible and experience either the control or intervention condition, but not both, and then provide an outcome measurement at follow-up. While most stepped wedge trials use simple randomisation, stratification and restricted randomisation are often feasible and may be useful. Some recent studies collect outcome information from individuals exposed a long time before or after the rollout period, but this contributes little to the primary analysis. Incomplete designs should be considered when the intervention cannot be implemented quickly. Carry-over effects can arise in stepped wedge trials with closed and open cohorts. Stepped wedge trial designs should be reported more clearly. Researchers should consider the use of stratified and/or restricted randomisation. Trials should generally not commit resources to collect outcome data from individuals exposed a long time before or after the rollout period. Though substantial carry-over effects are uncommon in stepped wedge trials, researchers should consider their possibility before conducting a trial with closed or open cohorts.Keywords
This publication has 23 references indexed in Scilit:
- The impact of the HEART risk score in the early assessment of patients with acute chest pain: design of a stepped wedge, cluster randomised trialBMC Cardiovascular Disorders, 2013
- Stepped wedge designs could reduce the required sample size in cluster randomized trialsJournal of Clinical Epidemiology, 2013
- Protocol-driven primary care and community linkages to improve population health in rural Zambia: the Better Health Outcomes through Mentoring and Assessment (BHOMA) projectBMC Health Services Research, 2013
- Mixed methods evaluation of targeted case finding for cardiovascular disease prevention using a stepped wedged cluster RCTBMC Public Health, 2012
- Effects of a free school breakfast programme on children's attendance, academic achievement and short-term hunger: results from a stepped-wedge, cluster randomised controlled trialJournal of Epidemiology and Community Health, 2012
- Will Mobile Diabetes Education Teams (MDETs) in primary care improve patient care processes and health outcomes? Study protocol for a randomized controlled trialTrials, 2012
- A cluster randomised stepped wedge trial to evaluate the effectiveness of a multifaceted information technology-based intervention in reducing high-risk prescribing of non-steroidal anti-inflammatory drugs and antiplatelets in primary medical care: The DQIP study protocolImplementation Science, 2012
- Quasi-experimental trial of diabetes Self-Management Automated and Real-Time Telephonic Support (SMARTSteps) in a Medicaid managed care plan: study protocolBMC Health Services Research, 2012
- Act In case of Depression: The evaluation of a care program to improve the detection and treatment of depression in nursing homes. Study ProtocolBMC Psychiatry, 2011
- Design and analysis of stepped wedge cluster randomized trialsContemporary Clinical Trials, 2007