J. Anim Sci.
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Published online first on October 23, 2006
J. Anim Sci. 1990. doi:10.2527/jas.2006-449
© 2006 American Society of Animal Science
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J. Anim Sci., doi: 10.2527/jas.2006-449
©Copyright, 2006, The American Society of Animal Science

ARTICLE

Statistical power calculations

Russell V. Lenth 1*

1 Department of Statistics and Actuarial Science, The University of Iowa, Iowa City, IA 52242

* To whom correspondence should be addressed. E-mail: russell-lenth{at}uiowa.edu.


  Abstract

This article focuses on how to do meaningful power calculations and sample-size determination for common study designs. There are three important guiding principles: 1) certain types of retrospective power calculations should be avoided, as they add no new information to an analysis; 2) effect size should be specified on the actual scale of measurement, not on a standardized scale, and 3) rarely can a definitive study be done without first doing a pilot study. Some simple examples as well as a complex example are given. Power calculations are illustrated using Java applets developed by the author.

Key Words: Statistical power, Sample size




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