Sample size estimation: How many individuals should be studied?

Research output: Contribution to journalReview articlepeer-review

401 Scopus citations


The number of individuals to include in a research study, the sample size of the study, is an important consideration in the design of many clinical studies. This article reviews the basic factors that determine an appropriate sample size and provides methods for its calculation in some simple, yet common, cases. Sample size is closely tied to statistical power, which is the ability of a study to enable detection of a statistically significant difference when there truly is one. A trade-off exists between a feasible sample size and adequate statistical power. Strategies for reducing the necessary sample size while maintaining a reasonable power will also be discussed.

Original languageEnglish (US)
Pages (from-to)309-313
Number of pages5
Issue number2
StatePublished - May 1 2003


  • Radiology and radiologists
  • Research Statistical analysis

ASJC Scopus subject areas

  • Radiology Nuclear Medicine and imaging


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