# Contingency Table

## CONTINGENCY TABLE

A contingency table is a display of data in columns and rows, arranged to facilitate the discovery of any relationship that may exist between different sets of data. The simplest type of contingency table displays two sets of data, one each in the columns and rows. The simplest of all is a fourfold, or 2 × 2, table. More complex contingency tables can be constructed with a further subclassification of data in the columns or rows, or in both columns and rows. Many varieties of data exist that can be arranged in this sort of table.

Some of the common variables that contingency tables show are: dichotomous (either-or); nominal (i.e. unordered, qualitative, classes, races); and ordinal (i.e. arranged along a scale that may or may not be continuous from zero to infinity, have defined upper and lower limits, or a defined mathematical relationship). Sometimes a relationship between columns and rows is intuitively obvious merely from inspection, and may show that the values in the columns and those in the rows vary either directly or inversely—that is, as the numbers increase across the rows, they also increase down the columns, or vice versa. At other times there may be no obvious relationship, but one may be revealed by appropriate statistical tests for association or correlation among the variables displayed in the table.

JOHN M. LAST