Pharmacy World and Science

, Volume 20, Issue 3, pp 113–117 | Cite as

Crossover studies are a better format for comparing equivalent treatments than parallel‐group studies.

  • Ton J.M. Cleophas
  • Ed M. de Vogel


Background: In controlled clinical trials the new treatment may be a slight modification of the standard or be equivalent to it with the addition of a new component. In this situation there is a positive correlation between the response to the new and the standard treatment. Objective: The influence of the correlation between the treatment responses on the statistical sensitivity of testing was studied. Randomized trials of equivalent treatments in psychiatry and hypertension research were studied for their design in relation to their level of correlation. Results: With equivalent treatments and, thus, a positive correlation a paired analysis provides better power than an unpaired one. Conclusions: Crossover studies are a better format than parallel‐group studies for comparing equivalent treatments. The scientific community is technically largely unaware of the mechanisms by which correlation levels influence or lack to influence the statistical power of controlled clinical trials.

Crossover studies Parallel‐group studies Equivalent treatments Correlation levels between treatment responses 


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Copyright information

© Kluwer Academic Publishers 1998

Authors and Affiliations

  • Ton J.M. Cleophas
    • 1
  • Ed M. de Vogel
    • 1
  1. 1.Departments of Medicine and Clinical PharmacyMerwede Hospital DordrechtDordrechtThe Netherlands

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