Statistics review 8: Qualitative data – tests of association

doi:10.1186/cc2428

Critical Care
Volume 8
Issue 1

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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 8: Qualitative data – tests of association

Viv Bewick¹ , Liz Cheek¹ and Jonathan Ball²

¹Senior Lecturer, School of Computing, Mathematical and Information Sciences, University of Brighton, Brighton, UK

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

author email corresponding author email

Critical Care 2004, 8:46-53doi:10.1186/cc2428


Published:	30 December 2003

Abstract

This review introduces methods for investigating relationships between two qualitative (categorical) variables. The χ²test of association is described, together with the modifications needed for small samples. The test for trend, in which at least one of the variables is ordinal, is also outlined. Risk measurement is discussed. The calculation of confidence intervals for proportions and differences between proportions are described. Situations in which samples are matched are considered.