2X2 TABLES

Fourfold (2 .times. 2) tables are used to describe enumeration data; they are concise and useful for summarizing many kinds of biomedical information. A familiar form is with 2 samples, each of which provides a 2-valued outcome or observation, such as lived-died, normal-abnormal. These tables may be from research designs of several types: cross-sectional surveys, prospective models, retrospective models, and randomized clinical trials. Several methods of analysis of 2 .times. 2 tables are discussed, without the mathematical detail: .chi.2 test, critical ratio test, Fisher''s exact test, and other less commonly used tests. The use of the relative risk ratio and the odds ratio to describe 2 .times. 2 tables is discussed. Some pitfalls in the use and interpretation of 2 .times. 2 tables are reviewed.