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ARTICLE |
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 |
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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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