Cluster randomised controlled trial

A cluster randomised controlled trial is a type of randomised controlled trial in which groups of subjects (as opposed to individual subjects) are randomised.[1] Cluster randomised controlled trials are also known as cluster randomised trials,[2] group-randomised trials,[3][4] and place-randomized trials.[5]

A 2004 bibliometric study documented an increasing number of publications in the medical literature on cluster randomised controlled trials since the 1980s.[1] Advantages of cluster randomised controlled trials over individually randomised controlled trials include:

  • The ability to study interventions that cannot be directed toward selected individuals (e.g., a radio show about lifestyle changes) and the ability to control for "contamination" across individuals (e.g., one individual's changing behaviors may influence another individual to do so).[6]
  • Reduced cost in running a survey. For example, when wanting to survey households, it could often be cheaper to choose street blocks and survey all the houses there in order to reduce the cost of traveling for the people conducting the survey.[7]
  • Sometimes due to data availability, it is only possible to do cluster sampling. For example, if wanting to survey households, it may be that there is no census list of houses (due to privacy restrictions of the Bureau of Statistics of the country). However, there may be a public record of street blocks and their addresses, and these can be used for creating the sampling frame.

Disadvantages compared with individually randomised controlled trials include greater complexity in design and analysis, and a requirement for more participants to obtain the same statistical power.[2] Specifically, the cluster randomised designs introduce dependence (or clustering) between individual units sampled. This effect depends on the Intraclass correlation, and the magnitude of the effect is measured using the design effect. An example would be an educational intervention in which schools are randomised to one of several new teaching methods. When comparing differences in outcome achieved under the new methods, researchers must account for the fact that two students sampled from a single school are more likely to be similar (in terms of outcomes) than two students sampled from different schools. Multilevel or similar statistical models are typically used to correct for this non-independence.

See also

References
  1. Bland JM (2004). "Cluster randomised trials in the medical literature: two bibliometric surveys". BMC Med Res Methodol. 4: 21. doi:10.1186/1471-2288-4-21. PMC 515302. PMID 15310402.
  2. Campbell MK, Elbourne DR, Altman DG, CONSORT group (2004). "CONSORT statement: extension to cluster randomised trials". BMJ. 328 (7441): 702–8. doi:10.1136/bmj.328.7441.702. PMC 381234. PMID 15031246.
  3. Murray DM, Varnell SP, Blitstein JL (2004). "Design and analysis of group-randomized trials: a review of recent methodological developments". Am J Public Health. 94 (3): 423–32. doi:10.2105/AJPH.94.3.423. PMC 1448268. PMID 14998806.
  4. Patton GC, Bond L, Carlin JB, Thomas L, Butler H, Glover S, Catalano R, Bowes G (2006). "Promoting social inclusion in schools: a group-randomized trial of effects on student health risk behavior and well-being". Am J Public Health. 96 (9): 1582–7. doi:10.2105/AJPH.2004.047399. PMC 1551970. PMID 16873760.
  5. Boruch R, May H, Turner H, Lavenberg J, Petrosino A, De Moya D, Grimshaw J, Foley E (2004). "Estimating the effects of interventions that are deployed in many places: place-randomized trials". American Behavioral Scientist. 47 (5): 608–633. doi:10.1177/0002764203259291.
  6. Edwards SJ, Braunholtz DA, Lilford RJ, Stevens AJ (1999). "Ethical issues in the design and conduct of cluster randomised controlled trials". BMJ. 318 (7195): 1407–9. doi:10.1136/bmj.318.7195.1407. PMC 1115783. PMID 10334756.
  7. Sampling People, Networks and Records coursers course (worth finding a better reference)

Further reading
  • Boruch RF. Place randomized trials: experimental tests of public policy. Thousand Oaks, CA: Sage Publications, 2005. ISBN 1-4129-2582-7
  • M. J. Campbell and S. J. Walters, 2014: How to Design, Analyse, and Report Cluster Randomised Trials. Wiley. ISBN 978-1-119-99202-8
  • A. Donner and N. Klar, 2000: Design and Analysis of Cluster Randomization Trials in Health Research. Arnold.
  • S. Eldridge and S. Kerry, 2012: A Practical Guide to Cluster Randomised Trials in Health Services Research. Wiley.
  • R. J. Hayes and L. H. Moulton, 2017: Cluster Randomised Trials. Second edition. Chapman & Hall.
  • Mosteller F, Boruch RF. Evidence matters: randomized trials in education research. Washington, DC: Brookings Institution Press, 2002. ISBN 0-8157-0204-3
  • Murray DM. Design and analysis of group-randomized trials. New York: Oxford University Press, 1998. ISBN 0-19-512036-1
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