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. Cluster randomised controlled trials are also known as cluster randomised trials, group-randomised trials, and place-randomized trials.
A 2004 bibliometric study documented an increasing number of publications in the medical literature on cluster randomised controlled trials since the 1980s. 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).
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. Specifically, the cluster randomised designs introduce dependence (or clustering) between individual units sampled. 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 
- 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. PMID 15310402.
- 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. PMID 15031246.
- 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. PMID 14998806.
- 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. PMID 16873760.
- 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". Am Behav Sci 47 (5): 608–633. doi:10.1177/0002764203259291.
- 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. PMID 10334756.
Further reading 
- Boruch RF. Place randomized trials: experimental tests of public policy. Thousand Oaks, CA: Sage Publications, 2005. ISBN 1-4129-2582-7
- 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, 2009: Cluster Randomised Trials. 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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