Statistics review 4: Sample size calculations

doi:10.1186/cc1521

Critical Care
Volume 6
Issue 4

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This article is part of a series on Medical statistics, edited by Jonathan Ball, Viv Bewick and Liz Cheek.

Review

Statistics review 4: Sample size calculations

Elise Whitley¹ and Jonathan Ball²

¹Lecturer in Medical Statistics, University of Bristol, Bristol, UK

²Lecturer in Intensive Care Medicine, St George's Hospital Medical School, London, UK

Critical Care 2002, 6:335-341doi:10.1186/cc1521


Published:	10 May 2002

Abstract

The present review introduces the notion of statistical power and the hazard of under-powered studies. The problem of how to calculate an ideal sample size is also discussed within the context of factors that affect power, and specific methods for the calculation of sample size are presented for two common scenarios, along with extensions to the simplest case.