Tables, Two-by-Two and Contingency

Contingency tables are used in medical research to organize summary data from research studies. The data are arranged in columns and rows according to two or more categorical variables. The term two-by-two (2 × 2) table is used to describe the specific contingency table that compares two dichotomous categorical variables and thus has two columns and two rows of data. Contingency tables are also sometimes called row-by-column tables, or R-by-C tables for short. Contingency tables efficiently display summary data about two or more categorical variables. A variety of statistical tests can be quickly calculated with the data contained in a contingency table.


The “classic” 2 × 2 table will have a dichotomous outcome variable labeled at the top of the two columns and a categorical exposure ...

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