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JAMA Guide to Statistics and Methods
March 1, 2019

Treatment Effects in Multicenter Randomized Clinical Trials

Author Affiliations
  • 1Luxembourg Institute of Health, Strassen, Luxembourg
  • 2Medical Statistics Group, ScHARR, The University of Sheffield, Sheffield, United Kingdom
  • 3Department of Emergency Medicine, Harbor-UCLA Medical Center, Torrance, California
  • 4Department of Emergency Medicine, David Geffen School of Medicine at UCLA, Los Angeles, California
  • 5Berry Consultants LLC, Austin, Texas
JAMA. Published online March 1, 2019. doi:10.1001/jama.2019.1480

It is common for treatments to be evaluated in clinical trials that involve many sites or centers, primarily because one center rarely can enroll sufficient numbers of patients to complete the trial.1 The use of multiple clinical sites introduces complexity because outcomes at different sites may be systematically different, eg, due to differences in patient populations, ancillary treatment practices, or other factors. Thus, appropriate statistical analyses of multicenter clinical trials consider these center effects to yield a better understanding of the overall mean treatment effect and the variability in treatment effects and patient outcomes among sites.1

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