A 1 degree of freedom
The shape of the c2 distribution changes according to the number of degrees of freedom (df) involved in a particular testing situation. Thus, in order to determine the correct p-value associated with a particular c2 value, it is necessary to know the correct degrees of freedom. For contingency tables, the correct degrees of freedom is obtained with the following formula: df = (r-1)(c-1), where r is the number of rows, and c is the number of columns. In a table with 2 rows and 2 columns, the c2 test will have 1 degree of freedom.