Sample size calculations for pilot randomized trials: a confidence interval approach

J Clin Epidemiol. 2013 Feb;66(2):197-201. doi: 10.1016/j.jclinepi.2012.09.002. Epub 2012 Nov 27.


Objectives: To describe a method using confidence intervals (CIs) to estimate the sample size for a pilot randomized trial.

Study design: Using one-sided CIs and the estimated effect size that would be sought in a large trial, we calculated the sample size needed for pilot trials.

Results: Using an 80% one-sided CI, we estimated that a pilot trial should have at least 9% of the sample size of the main planned trial.

Conclusion: Using the estimated effect size difference for the main trial and using a one-sided CI, this allows us to calculate a sample size for a pilot trial, which will make its results more useful than at present.

Publication types

  • Comparative Study
  • Review

MeSH terms

  • Confidence Intervals*
  • Evidence-Based Medicine / standards
  • Female
  • Humans
  • Male
  • Pilot Projects*
  • Practice Guidelines as Topic / standards*
  • Randomized Controlled Trials as Topic*
  • Research Design
  • Sample Size
  • Statistics as Topic
  • United Kingdom