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Observational Study

  1. Mitchell H. Gail

Published Online: 15 JUL 2005

DOI: 10.1002/0470011815.b2a03089

Encyclopedia of Biostatistics

Encyclopedia of Biostatistics

How to Cite

Gail, M. H. 2005. Observational Study. Encyclopedia of Biostatistics. 6.

Author Information

  1. National Cancer Institute, Bethesda, MD, USA

Publication History

  1. Published Online: 15 JUL 2005


An observational study is a study in which conditions are not under the control of the investigator, unlike an experimental study. Because randomization of exposure levels is not part of an observational study, associations with exposure may result from confounding by factors associated both with exposure and health outcome.


  • observational study;
  • experimental study;
  • confounding