Statistical power, sample sizes, and the software to calculate them easily

Abstract

Many authors have advocated the use of power analysis for designing more sensitive and efficient ecological studies. However, few manuscripts report using power analysis for improving the study design, perhaps because of the wide range of tests routinely used by most ecologists and the limitations of most power analysis software. UnifyPow, an excellent freeware macro that runs within SAS, easily and accurately calculates power or sample sizes for a wide range of statistical tests for a broad range of statistical models. Despite its potential contribution to the field, UnifyPow is virtually unused by ecologists. Perhaps this is because UnifyPow was developed by medical statisticians or because there is no manual, although there is extensive online documentation. I briefly review the flexibility and breadth of UnifyPow; describe how it works; and, using ecological examples, demonstrate how to use it to calculate power for an extremely wide range of statistical tests. © 2006 American Institute of Biological Sciences.