Hypothesis Testing and Effect Size Estimation in Clinical Trials

Learning Objectives: This paper provides the reader with an overview of several key elements in study planning and analysis. In particular, it highlights the differences between significance tests (statistical significance) and effect size estimation (clinical significance).

Data Sources: This paper focuses on methodologic issues, and provides an overview of trends in research. PAPER SELECTION: References were selected to provide a cross-section of the approaches currently being used. The paper also discusses a number of logical fallacies that have been cited as examples in earlier papers on research design.

Conclusions: Significance tests are intended solely to address the viability of the null hypothesis that a treatment has no effect, and not to estimate the magnitude of the treatment effect. Researchers are advised to move away from significance tests and to present instead an estimate of effect size bounded by confidence intervals. This approach incorporates all the information normally included in a test of significance but in a format that highlights the element of interest (clinical significance rather than statistical significance). This approach should also have an impact on study planning--a study should have enough power to reject the null hypothesis and also to yield a precise estimate of the treatment effect.