A common procedure for detecting DIF is the Mantel-Haenszel (MH) approach. The MH procedure is a chi-squared contingency table based approach which examines differences between the reference and focal groups on all items of the test, one by one. The ability continuum, defined by total test scores, is divided into "k" intervals which then serves as the basis for matching members of both groups. A 2 x 2 contingency table is used at each interval of "k" comparing both groups on an individual item. The rows of the contingency table correspond to group membership (reference or focal) while the columns correspond to correct or incorrect responses. The following table presents the general form for a single item at the "k"th ability interval.