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  1. Willi Sauerbrei

Published Online: 14 DEC 2007

DOI: 10.1002/9780471462422.eoct355

Wiley Encyclopedia of Clinical Trials

Wiley Encyclopedia of Clinical Trials

How to Cite

Sauerbrei, W. 2007. Covariates. Wiley Encyclopedia of Clinical Trials. 1–13.

Author Information

  1. University Medical Center Freiburg, Institute of Medical Biometry and Medical Informatics, Freiburg, Germany

Publication History

  1. Published Online: 14 DEC 2007


The central role of covariates for several issues in clinical research and patient management is discussed. In clinical trials covariates are used to define the patient population, to allocate treatment in a randomized trial, to adjust the estimate of a treatment effect, and to define subgroups for the investigation of interactions. Furthermore, we will discuss the issue of categorization or determination of the functional relationship to describe the influence of a continuous covariate on an outcome of interest. Some issues of reporting and of the summary assessments of prognostic markers are discussed in the last section. (The issues of analyzing a prognostic marker study are discussed elsewhere.) To further increase and improve the use of covariate data of individual patients, it is important to have reliable measurements and to analyze the data and their interrelationships with the most suitable statistical approach. Often, this will require a close collaboration between clinicians and statisticians.