Stepped-wedge trial

A stepped-wedge trial is a form of randomised controlled trial that involves sequential but random rollout of an intervention over multiple time periods. The term "stepped wedge" was coined by the Gambia Hepatitis Intervention Study due to the stepped-wedge shape that is apparent from a schematic illustration of the design.[1] The crossover is in one direction, typically from control to intervention, with the intervention not removed once implemented. The stepped-wedge design can be used for individually randomised trials,[2][3] but is more commonly used as a cluster randomised trial (CRT).[4]

In the context of a cluster randomised trial, the stepped-wedge design involves the collection of observations at a baseline period in which no clusters are exposed to the intervention. Following this, at regular intervals, or steps, a cluster (or group of clusters) is randomised to receive the intervention.[4][5] This process continues until all clusters have crossed over to receive the intervention. Observations are taken at every cluster and at each time period.[6] Stepped-wedge studies typically have one time period in which observations are made while all clusters are unexposed to the intervention, and one time period in which all clusters are exposed to the intervention.

In a stepped-wedge CRT, more clusters are exposed to the intervention at later than earlier time periods. As such, it is possible that an underlying temporal trend may confound the intervention effect, and so the confounding effect of time must be accounted for in both pre-trial power calculations and post-trial analysis [4][7][8]

The design and analysis of stepped-wedge trials is therefore more complex than for other types of randomised trials. Previous systematic reviews highlighted the poor reporting of sample size calculations and a lack of consistency in the analysis of such trials.[4][5] Hussey and Hughes were the first authors to suggest a structure and formula for estimating power in stepped-wedge studies in which data was collected at each and every step.[6] This has now been expanded for designs in which observations are not made at each step as well as multiple layers of clustering.[9] Additionally, a design effect (used to inflate the sample size of an individually randomised trial to that required in a cluster trial) has been established,[10] which has shown that the stepped wedge CRT could reduce the number of patients required in the trial compared to other designs. [10][11][12]


References

  1. ↑ The Gambia Hepatitis Study Group, The Gambia Hepatitis Intervention Study, Cancer Research, 1987;47(21):5782–87.
  2. ↑ Ratanawongsa N, Handley MA, Quan J, Sarkar U, Pfeifer K, Soria C, et al, Quasi-experimental trial of diabetes Self-Management Automated and Real-Time Telephonic Support (SMARTSteps) in a Medicaid managed care plan: study protocol., BMC health services research, 2012;12:22.
  3. ↑ Lohaugen GCC, Beneventi H, Andersen GL, Sundberg C, Ostgard HF, Bakkan E, et al., Do children with cerebral palsy benefit from computerized working memory training? Study protocol for a randomized controlled trial., Trials, 2014;15(1).
  4. 1 2 3 4 Brown CA, Lilford RJ. The stepped wedge trial design: a systematic review. BMC medical research methodology. 2006;6:54.
  5. 1 2 Mdege ND, Man MS, Taylor Nee Brown CA, Torgerson DJ. Systematic review of stepped wedge cluster randomized trials shows that design is particularly used to evaluate interventions during routine implementation. Journal of clinical epidemiology. 2011;64(9):936–48.
  6. 1 2 Hussey MA, Hughes JP. Design and analysis of stepped wedge cluster randomized trials. Contemp Clin Trials. 2007;28(2):182–91
  7. ↑ Van den Heuvel ER, Zwanenburg RJ, Van Ravenswaaij-Arts CM. A stepped wedge design for testing an effect of intranasal insulin on cognitive development of children with Phelan-McDermid syndrome: A comparison of different designs. Statistical methods in medical research. 2014.
  8. ↑ Hemming K, Haines TP, Chilton PJ, Girling AJ, Lilford RJ. The stepped wedge cluster randomised trial: rationale, design, analysis, and reporting. BMJ (Clinical research ed). 2015;350:h391.
  9. ↑ Hemming K, Lilford R, Girling AJ. Stepped-wedge cluster randomised controlled trials: a generic framework including parallel and multiple-level designs. Statistics in medicine. 2015;34(2):181–96.
  10. 1 2 Woertman W, de Hoop E, Moerbeek M, Zuidema SU, Gerritsen DL, Teerenstra S. Stepped wedge designs could reduce the required sample size in cluster randomized trials. Journal of clinical epidemiology. 2013;66(7):752–58.
  11. ↑ de Hoop E, Woertman W, Teerenstra S. The stepped-wedge cluster randomized trial always requires fewer clusters but not always fewer measurements (participants) than a parallel cluster randomized trial in a cross-sectional design. In reply. Journal of clinical epidemiology. 2013;66(12):1428.
  12. ↑ Keriel-Gascou M, Buchet-Poyau K, Rabilloud M, Duclos A, Colin C. A stepped wedge cluster randomized trial is preferable for assessing complex health interventions. Journal of clinical epidemiology. 2014;67(7):831–33.
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