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

Bibliometrics

Bibliometrics is a set of methods to quantitatively analyze scientific and technological literature. Citation analysis and content analysis are commonly used bibliometric methods...

 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

Statistical power

The power of a statistical test is the probability that the test will reject the null hypothesis when the null hypothesis is actually false . The power is in general a function of the possible distributions, often determined by a parameter, under the alternative hypothesis...

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Further reading

• Murray DM. Design and analysis of group-randomized trials. New York: Oxford University Press, 1998. ISBN 0195120361
• Mosteller F, Boruch RF. Evidence matters: randomized trials in education research. Washington, DC: Brookings Institution Press, 2002. ISBN 0815702043
• Boruch RF. Place randomized trials: experimental tests of public policy. Thousand Oaks, CA: Sage Publications, 2005. ISBN 1412925827