Lesson 6: Sample Size and Power - Part B

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This week we continue exploring the issues of sample size and power, this time with regard to the differing purposes of clinical trials. Often the objective of the trial is to establish that a therapy is efficacious, but what is the proper control group? Can superiority to placebo be clearly established when there are other effective therapies on the market? These questions lead to special considerations based on whether the trial has an objective of establishing superiority, equivalence or non-inferiority. So, let’s move ahead…

Learning objectives & outcomes

Upon completion of this week's lessons, you should be able to do the following:

  • Distinguish between superiority, non-inferiority and equivalence trials in terms of
    • objectives
    • control group
    • hypotheses tested and
    • formation of confidence intervals.
  • Recognize characteristics of a clinical trial with high external validity
  • Define which data are included in an intention-to-treat analysis
  • Recognize the major considerations for designing an equivalence or non-inferiority trial.
  • Perform sample size calculations for some equivalence and non-inferiority trials, using SAS programs.


Berger RL, Hsu JC. Bioequivalence trials, intersection-union tests, and equivalence confidence sets. Statistical Science 1996, 11: 283-319).

Piantadosi Steven. (2005) Sample size and power. In: Piantadosi Steven. Clinical Trials: A Methodologic Perspective. 2nd ed. Hoboken, NJ: John Wiley and Sons, Inc.