John Eng, M.D.
Russell H. Morgan Department of Radiology and Radiological Science
Johns Hopkins University School of Medicine, Baltimore, Maryland, USA
Computer requirements for this page: A reasonably up-to-date web browser
Please send any bugs, questions, comments, or suggestions to
All electronic mail will be answered.
Instructions: This page calculates the sample size for four simple study designs. The equations
are discussed more fully in Ref. 1, and this web page is intended to accompany that article. To estimate
a sample size, identify the equation appropropriate to your study design. Enter values for the parameters
under "Input Values" and click the corresponding "Calculate" button. See
below for program development details, acknowledgments,
and a list of references.
Program Development Details and Acknowledgments: This page uses normsdist.js,
a small library that supplies numerical functions for performing
programming language to enable its use over the
web. Ref. 2 documents the algorithm for normsdist.js's inverse normal distribution routine, which is used
to calculate Eqs. 1 and 2.
Eng J. Sample size estimation: how many individuals should be studied? Radiology 2003; 227: 309-313.