title: Understanding statistical power.
abstract: This article provides an introduction to power analysis so that readers have a basis for understanding the importance of statistical power when planning research and interpreting the results. A simple hypothetical study is used as the context for discussion. The concepts of false findings and missed findings are introduced as a way of thinking about type I and type II errors. The primary factors that affect power are described and examples are provided. Finally, examples are presented to demonstrate 2 uses of power analysis, 1 for prospectively estimating the sample size needed to insure finding effects of a known magnitude in a study and 1 for retrospectively estimating power to gauge the likelihood that an effect was missed.
authors: Program in Physical Therapy, Washington University, St. Louis, MO 63108-2212, USA. nortonb@msnotes.wustl.edu
authors: B J
authors: BJ
authors: Norton
authors: M J
authors: MJ
authors: Strube
mesh_terms: D003627:Data Interpretation, Statistical; D006801:Humans; D015588:Observer Variation; D012107:Research Design; D018401:Sample Size; D016008:Statistical Distributions