Fourfold (2 X 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 two samples, each of which provides a two-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 X 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 X 2 tables is discussed. Some pitfalls in the use and interpretation of 2 X 2 tables are reviewed.
四格表（2×2表）用于描述计数资料；它们简洁明了，有助于汇总多种生物医学信息。一种常见的形式是有两个样本，每个样本都提供一个二值结果或观察值，如存活-死亡、正常-异常。这些表格可能来自几种类型的研究设计：横断面调查、前瞻性模型、回顾性模型和随机临床试验。本文讨论了几种分析2×2表的方法，但不涉及数学细节：卡方检验、临界比检验、费舍尔精确检验以及其他较少使用的检验。还讨论了用相对危险度比和比值比来描述2×2表的情况。回顾了在使用和解释2×2表时的一些陷阱。
