Comprehensive Software for Sample-Size Analysis

Various software applications now offer ever-greater functionality for assessing statistical power and choosing appropriate sample sizes. Among these are nQuery Advisor, PASS, and Power and Precision (a.k.a. Sample Power), all commercial products that run under MS Windows. In addition, UnifyPow is a freeware macro for the SAS System, which runs on many platforms. These "power-full" tools give researchers markedly enhanced capabilities and thus a greater responsibility to plan their studies more rigorously. Performing sample-size analyses forces researchers to formulate not only their research questions, design, and primary outcome measures, but also their specific statistical hypotheses and analysis methods.

This workshop will first review and discuss core principles and issues involved in power analysis. But most of the day will be spent studying realistic examples of statistical planning, demonstrating how UnifyPow and, at times, the other products can be used to handle a wide variety of designs and methods. Mathematical theory and details about computing algorithms will not be stressed. While primary focus will be on choosing sample sizes in order to assure adequate power for typical hypothesis testing, analogous considerations will also be given to assuring sufficiently tight confidence intervals and strong tests of equivalence. Most of the day will focus on common data analysis methods. The software will be demonstrated live and will be available for at least limited hands-on use. For more information, visit the following web sites:

nQuery Advisor
Power and Precision

Ralph O'Brien

Ralph O'Brien, PhD (1975, University of North Carolina at Chapel Hill) is the creator and author of UnifyPow. He has served on the faculties and computing center staffs of the Universities of Virginia and Tennessee, he was Director of Biostatistics at the University of Florida, and he was a member of the Behavioral Medicine Study Section for the National Institutes of Health.

He is now at the Cleveland Clinic Foundation, where he directs a large group of biostatisticians and programmers who support Foundation projects that altogether lead to almost 2000 publications per year. In addition to his work in power analysis, Ralph is also the creator of O'Brien's test for equality of variances, a method now available in the regular SAS System (via PROC GLM), as well as in JMP for Windows and Macs. For more, visit Ralph's home page.