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Primer: measuring the effects of treatment in clinical trials

Nature Clinical Practice Rheumatology volume 3, pages 291–297 (2007)Cite this article

Abstract

The results of clinical trials are often used as the basis for changes in clinical practice. Proper execution and interpretation of the results of trials are, therefore, of paramount importance to the welfare of patients. The results of a clinical trial are based on four key elements: the choice of the primary study end point, the method used to compare end points between groups, the clinically meaningful difference in the primary end point selected a priori by the investigators, and the power of the study to detect as statistically significant a difference between groups that is as large as the preselected clinically meaningful difference. These key elements directly follow from the primary hypothesis tested by the trial. This article reviews the basic features of these four elements, and the influence they have on the interpretation of clinical trials.

Key Points

  • Clinical trials should designate one clinical measure that is most relevant to the condition and treatment being studied as the primary end point

  • Effect sizes are useful unit-free measures of treatment effect, calculated as the change in the primary end point divided by its SD at baseline

  • The target treatment effect is the minimum degree of change that the trial is designed to detect as significantly different between the treatment groups, on the basis of a clinically meaningful difference in the primary end point

  • Levels of type I and type II statistical error indicate the likelihood that the trial results will be false positive or false negative

  • Post hoc subgroup comparisons should only be considered hypothesis-generating

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Acknowledgements

This work was supported by the Intramural Research Program, National Institute of Arthritis and Musculoskeletal and Skin Diseases, National Institutes of Health.

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  1. Building 10 CRC, Room 4-1339, 10 Center Drive, MSC 1468, Bethesda, MD 20892, USA wardm1@mail.nih.gov

Authors and Affiliations

  1. MM Ward is an Investigator at the Intramural Research Program, National Institute of Arthritis and Musculoskeletal and Skin Disease, National Institutes of Health, Bethesda, MD, USA.,

    Michael M Ward

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The author declares no competing financial interests.

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Ward, M. Primer: measuring the effects of treatment in clinical trials. Nat Rev Rheumatol 3, 291–297 (2007). https://doi.org/10.1038/ncprheum0478

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