Below are links to journal articles, arranged under broad headings, for readers who want to immerse themselves (or just paddle around) in the literature on stepped wedge trials. This is a hand-picked selection rather than an exhaustive review.
For a gentle introduction, read the blog posts first!
When following links to journal articles, note that some journals will require an institutional login or subscription.
- The Gambia Hepatitis Intervention Study (the first stepped wedge trial)
- Understanding stepped wedge trials
- Ethics and the stepped wedge trial
- Shortcomings of published stepped wedge trials
- Sample size calculation for stepped wedge trials
- Challenges with small numbers of clusters
- Analysis of stepped wedge trials: essentials
- Analytical approaches aimed at robustness
- Optimal designs and design variations
- Decaying intracluster correlation
The Gambia Hepatitis Intervention Study (the first stepped wedge trial)
World Health Organization (1983). Prevention of liver cancer : report of a WHO meeting [held in Geneva from 30 January to 4 February 1983]. Available here.
The Gambia Hepatitis Study Group. The Gambia Hepatitis Intervention Study. Cancer Res 1987;47(21):5782-7.
van der Sande MAB, Waight PA, Mendy M, et al. Long-Term Protection against HBV Chronic Carriage of Gambian Adolescents Vaccinated in Infancy and Immune Response in HBV Booster Trial in Adolescence. PLoS One 2007;8:e753.
Viviani S, Carrieri P, Bah E, et al. 20 years into the Gambia Hepatitis Intervention Study: assessment of initial hypotheses and prospects for evaluation of protective effectiveness against liver cancer. Cancer Epidemiol Biomarkers Prev 2008;17(11):3216-23.
Peto TJ, Mendy ME, Lowe Y, et al. Efficacy and effectiveness of infant vaccination against chronic hepatitis B in the Gambia Hepatitis Intervention Study (1986–90) and in the nationwide immunisation program. BMC Infect Dis 2014;14:7.
Understanding stepped wedge trials
Hemming K, Haines T P, Chilton P J, et al. The stepped wedge cluster randomised trial: rationale, design, analysis, and reporting BMJ 2015;350:h391.
Prost A, Binik A, Abubakar I, et al. Logistic, ethical, and political dimensions of stepped wedge trials: critical review and case studies. Trials 2015;16:351.
Hargreaves JR, Copas AJ, Beard E, et al. Five questions to consider before conducting a stepped wedge trial. Trials 2015;16:350.
Copas AJ, Lewis JJ, Thompson JA, et al. Designing a stepped wedge trial: three main designs, carry-over effects and randomisation approaches. Trials 2015;16:352.
Hemming K, Taljaard M, McKenzie J, et al. Reporting of stepped wedge cluster randomised trials: extension of the CONSORT 2010 statement with explanation and elaboration. BMJ 2018;363:k1614.
Hemming K, Taljaard M. Reflection on modern methods: when is a stepped wedge cluster randomized trial a good design choice? Int J Epidemiol 2020;49(3):1043-1052.
Hooper R. Key concepts in clinical epidemiology: Stepped wedge trials. J Clin Epidemiol 2021;137:159-162.
Hooper R, Eldridge SM. Cutting edge or blunt instrument: how to decide if a stepped wedge design is right for you. BMJ Quality & Safety 2021;30:245-250.
Ethics and the stepped wedge trial
Weijer C, Grimshaw JM, Eccles MP et al. The Ottawa Statement on the Ethical Design and Conduct of Cluster Randomized Trials. PLoS Med 2012;9(11).
Binik A. Delaying and withholding interventions: ethics and the stepped wedge trial. J Med Ethics 2019;45:662-667.
Shortcomings of published stepped wedge trials
Martin J, Taljaard M, Girling A, Hemming K. Systematic review finds major deficiencies in sample size methodology and reporting for stepped-wedge cluster randomised trials. BMJ Open 2016;6:e010166.
Taljaard M, Hemming K, Shah L, et al. Inadequacy of ethical conduct and reporting of stepped wedge cluster randomized trials: Results from a systematic review. Clin Trials 2017;14(4):333-341.
Eichner FA, Groenwold RHH, Grobbee DE, Rengerink KO. Systematic review showed that stepped-wedge cluster randomized trials often did not reach their planned sample size. J Clin Epidemiol 2019;107:89-100.
Caille A, Taljaard M, Le Vilain-Abraham F, et al. Recruitment and implementation challenges were common in stepped-wedge cluster randomized trials. J Clin Epidemiol 2022;148:93-103.
Nevins P, Ryan M, Davis-Plourde K, et al. Adherence to key recommendations for design and analysis of stepped-wedge cluster randomized trials: A review of trials published 2016–2022. Clin Trials. 2024;21(2):199-210.
Sample size calculation for stepped wedge trials
Hooper R, Bourke L. Cluster randomised trials with repeated cross sections: alternatives to parallel group designs. BMJ 2015;350:h2925.
Hooper R, Teerenstra S, de Hoop E, Eldridge S. Sample size calculation for stepped wedge and other longitudinal cluster randomised trials. Stat Med 2016;35:4718-4728.
Teerenstra, Taljaard, Haenen, et al. Sample size calculation for stepped-wedge cluster-randomized trials with more than two levels of clustering. Clin Trials 2019;16:225-236.
Kasza J, Hooper R, Copas A, Forbes AB. Sample size and power calculations for open cohort longitudinal cluster randomized trials. Stat Med 2020;39(13):1871-1883.
Hemming K, Kasza J, Hooper R, et al. A tutorial on sample size calculation for multiple-period cluster randomized parallel, cross-over and stepped-wedge trials using the Shiny CRT Calculator. Int J Epidemiol 2020;49(3):979-995.
Ouyang Y, Li F, Preisser JS, Taljaard M. Sample size calculators for planning stepped-wedge cluster randomized trials: a review and comparison. Int J Epidemiol. 2022;51(6):2000-2013.
Challenges with small numbers of clusters
Li P, Redden DT. Comparing denominator degrees of freedom approximations for the generalized linear mixed model in analyzing binary outcome in small sample cluster-randomized trials. BMC Med Res Methodol 2015;15:38.
Barker D, McElduff P, D’Este C, Campbell MJ. Stepped wedge cluster randomised trials: a review of the statistical methodology used and available. BMC Med Res Methodol 2016;16:69.
Taljaard M, Teerenstra S, Ivers NM et al. Substantial risks associated with few clusters in cluster randomized and stepped wedge designs. Clin Trials 2016;13(4):459-463.
Huang S, Fiero MH, Bell ML. Generalized estimating equations in cluster randomized trials with a small number of clusters: Review of practice and simulation study. Clin Trials 2016;13(4):445-449.
Barker D, D’Este C, Campbell MJ, McElduff P. Minimum number of clusters and comparison of analysis methods for cross sectional stepped wedge cluster randomised trials with binary outcomes: A simulation study. Trials 2017;18(1):119.
Leyrat C, Morgan KE, Leurent B et al. Cluster randomized trials with a small number of clusters: Which analyses should be used? Int J Epidemiol 2018;47(1):321–31.
Ford WP, Westgate PM. Maintaining the validity of inference in small-sample stepped wedge cluster randomized trials with binary outcomes when using generalized estimating equations. Stat Med 2020;39(21):2779–92.
Chaussee EL, Dickinson LM, Fairclough DL. Evaluation of a covariate-constrained randomization procedure in stepped wedge cluster randomized trials. Contemp Clin Trials 2021;105:106409.
Thompson J, Hemming K, Forbes A, et al. Comparison of small-sample standard-error corrections for generalised estimating equations in stepped wedge cluster randomised trials with a binary outcome: A simulation study. Stat Methods Med Res 2021;30(2):425-439.
Lee, K.M., Cheung, Y.B. The fixed-effects model for robust analysis of stepped-wedge cluster trials with a small number of clusters and continuous outcomes: a simulation study. Trials 2024;25:718.
Tong G, Nevins P, Ryan M, et al. A review of current practice in the design and analysis of extremely small stepped-wedge cluster randomized trials. Clin Trials. 2025;22(1):45-56.
Hemming K, Thompson J, Kristunas C et al. The performance of small sample correction methods for controlling type I error when analyzing parallel cluster randomized trials: a systematic review of simulation studies. J Clin Epidemiol 2025;185:111838.
Analysis of stepped wedge trials: essentials
Bond S. Theory of general balance applied to step wedge designs. Stat Med 2019;38(2):184-191.
Li F, Hughes JP, Hemming K, Taljaard M, Melnick ER, Heagerty PJ. Mixed-effects models for the design and analysis of stepped wedge cluster randomized trials: An overview. Stat Methods Med Res 2021;30(2):612-639.
Analytical approaches aimed at robustness
Thompson JA, Davey C, Fielding K, et al. Robust analysis of stepped wedge trials using cluster-level summaries within periods. Stat Med 2018;37:2487-500.
Thompson J, Davey C, Hayes R, et al. Permutation tests for stepped-wedge cluster-randomized trials. Stata J 2019;19:803-819.
Kennedy-Staffer L, de Gruttola V, Lipsitch M. Novel methods for the analysis of stepped wedge cluster randomised trials. Stat Med 2020;39:815-844.
Voldal EC, Kenny A, Xia F, Heagerty P, Hughes JP. Robust analysis of stepped wedge trials using composite likelihood models. Stat Med 2024;43(17):3326-3352.
Optimal designs and design variations
Lawrie J, Carlin JB, Forbes AB. Optimal stepped wedge designs. Statistics & Probability Letters 2015;99:210-214.
Girling, A. J., and Hemming, K. Statistical efficiency and optimal design for stepped cluster studies under linear mixed effects models. Stat Med 2016;35:2149–2166.
Hooper R, Copas A. Stepped wedge trials with continuous recruitment require new ways of thinking. J Clin Epidemiol 2019;116:161-166.
Hooper R, Kasza J, Forbes A. The hunt for efficient, incomplete designs for stepped wedge trials with continuous recruitment and continuous outcome measures. BMC Med Res Methodol 2020;20(1):279.
Hooper R, Copas AJ. Optimal design of cluster randomised trials with continuous recruitment and prospective baseline period. Clin Trials 2021;18(2):147-157.
Kasza J, Bowden R, Hooper R, Forbes AB. The batched stepped wedge design: A design robust to delays in cluster recruitment. Stat Med 2022;41(18):3627-3641.
Watson SI, Girling A, Hemming K. Optimal study designs for cluster randomised trials: An overview of methods and results. Stat Methods Med Res 2023;32(11):2135-2157.
Rezaei-Darzi E, Grantham KL, Forbes AB, et al. The impact of iterative removal of low-information cluster-period cells from a stepped wedge design. BMC Med Res Methodol 2023;23:160.
Grantham KL, Forbes AB, Hooper R, Kasza J. The staircase cluster randomised trial design: A pragmatic alternative to the stepped wedge. Stat Methods Med Res 2024;33(1):24-41.
Hooper R, Quintin O, Kasza J. Efficient designs for three-sequence stepped wedge trials with continuous recruitment. Clin Trials 2024;21(6):723-733.
Decaying intracluster correlation
Kasza J, Hemming K, Hooper R, et al. Impact of non-uniform correlation structure on sample size and power in multiple-period cluster randomised trials. Stat Methods Med Res 2019;28(3):703-716.
Li F. Design and analysis considerations for cohort stepped wedge cluster randomized trials with a decay correlation structure. Stat Med 2020;39:438–455.
Rezaei-Darzi E, Kasza J, Forbes A, Bowden R. Use of information criteria for selecting a correlation structure for longitudinal cluster randomised trials. Clin Trials. 2022;19(3):316-325.
Kasza J, Bowden R, Ouyang Y, et al. Does it decay? Obtaining decaying correlation parameter values from previously analysed cluster randomised trials. Stat Methods Med Res 2023;32(11):2123-2134.
Ouyang, Y., Kulkarni, M.A., Protopopoff, N. et al. Accounting for complex intracluster correlations in longitudinal cluster randomized trials: a case study in malaria vector control. BMC Med Res Methodol 2023;23:64.
More
If you have read all the way to the bottom of this reading list and still want to know more about stepped wedge trials, here is a link to my NIHR Methods Academy webinar: