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(Circulation. 2002;105:3062.)
© 2002 American Heart Association, Inc.

Current Perspective

Defending the Rationale for the Two-Tailed Test in Clinical Research

Lemuel A. Moyé, MD, PhD; Alan T.N. Tita, MD, MPH

From The University of Texas Houston Health Science Center, School of Public Health (L.A.M., A.T.N.T.), and Department of Obstetrics and Gynecology, Baylor College of Medicine (A.T.N.T.), Houston, Tex.

Correspondence to Lemuel A. Moyé, MD, PhD, RAS Building E815, 1200 Herman Pressler, Houston, TX 77030. E-mail lmoye@utsph.sph.uth.tmc.edu

Key Words: statistics • tests • trials

An extract of the first 250 words of the full text is provided, because this article has no abstract.

	Introduction

 
The issue of one-sided versus two-sided hypothesis testing in clinical trial analyses has been the subject of debate in the medical and statistical literature.^1–4 This design consideration represents a sharp divide in the research community, separating the investigators’ deep-seated beliefs in therapy effectiveness from their obligatory primary concern for patient welfare. In a recent commentary, Knottnerus and Bouter⁵ advanced the theory that, for individual trials evaluating new interventions not previously studied, a one-sided hypothesis test seems sensible from both an ethical and cost-efficiency perspective. Certainly, to many healthcare researchers, the temptation of one-tailed hypothesis testing, in which the location of type I errors coincides exactly with the investigator’s prospective intuition (based on available but sometimes misleading information) about the research result, can be difficult to resist. For a specified experimental probability of type I error, the allure of the smaller sample size associated with one-tailed testing further strengthens its attraction for some researchers. We argue here, however, that one-tailed testing should be avoided in healthcare research for ethical and cost-efficiency reasons, especially in randomized trials in which the investigator controls the intervention. Rather than reflecting the investigators’ a priori intuition, the type I error should reflect the uncertainty of the research effort’s future conclusions. This is critical in a field in which healthcare practitioners and healthcare researchers can inadvertently do harm to their patients.

	One-Sided Thinking and Ethical Restraints

 
In clinical intervention trials, we as investigators wish to demonstrate that the tested intervention is beneficial. As clinical researchers, we do not like to harbor the . . . [Full Text of this Article]