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Contemp Clin Trials. 2007 Jul;28(4):451-8. Epub 2006 Nov 17.

Sample size calculation for multicenter randomized trial: taking the center effect into account.

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INSERM CIC 202, Université François Rabelais, Tours, CHRU de Tours, France.


In multicenter trials, data from the same center are more similar than those from different centers. These similarities induce a correlation between data, known as the center effect, which is assessed by the intraclass correlation coefficient (ICC). Here, we derive a sample size formula for continuous data that takes into account this center effect. Our analytical developments lead to an elementary formula different from the classical one by a (1-rho) factor, where rho is the ICC. This work allows for adjusting and reducing the sample size according to the magnitude of the center effect and leads to a better consistency in the conduct of multicenter randomized trials.

[Indexed for MEDLINE]

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