7. Clinical Trials

  1. Thomas P. Ryan

Published Online: 27 JUN 2013

DOI: 10.1002/9781118439241.ch7

Sample Size Determination and Power

Sample Size Determination and Power

How to Cite

Ryan, T. P. (2013) Clinical Trials, in Sample Size Determination and Power, John Wiley & Sons, Inc., Hoboken, NJ, USA. doi: 10.1002/9781118439241.ch7

Author Information

  1. Institute for Statistics Education, Arlington, Virginia and Northwestern University, Evanston, Illinois

Publication History

  1. Published Online: 27 JUN 2013
  2. Published Print: 26 JUL 2013

ISBN Information

Print ISBN: 9781118437605

Online ISBN: 9781118439241



  • Bayesian methods;
  • clinical trials;
  • cluster randomized trials;
  • competing probability;
  • power;
  • sample size determination;
  • software


There are special considerations that must be made in determining sample size when the subjects are people, including the dropout rate and ethical considerations. Although the FDA requires two clinical trials before approval of a new drug can be granted, under certain conditions a single clinical trial will suffice. There is usually a progression from Phase I to Phase II if only a specified minimum number of patients respond favorably to the drug. Phase III is intended to provide a definitive assessment of efficacy, often involving thousands of patients. Cluster randomized trials are often used in the health field. Other topics discussed include the use of power in clinical studies; pharmacodynamic, pharmacokinetic, and pharmacogenetic experiments; method of competing probability; cost and other sample size determination methods; and meta-analyses of clinical trials. Software for sample size determination for clinical trials using Bayesian methods has not existed in the recent past.

Controlled Vocabulary Terms

cluster randomised controlled trial