A contingency table is a way of summarising the relationship between variables, each of which can take only a small number of values. It is a table of frequencies classified according to the values of the variables in question. When a population is classified according to two variables it is said to have been 'cross-classified' or subjected to a two-way classification. Higher classifications are also possible. ********************* A contingency table is used to summarise categorical data. It may be enhanced by including the percentages that fall into each category. What you find in the rows of a contingency table is contingent upon (dependent upon) what you find in the columns.
A table (usually 2 rows and 2 columns) that is often used in epidemiology to show the relationship between disease and exposure. The table can be used to divide persons into the categories of diseased and exposed (a), diseased and not exposed (b), not diseased and exposed (c), and not diseased and not exposed (d): Exposure Yes No Disease Yes No
Table with numbers in each cell determined by jointly considering the two joint categories