Differential Person Functioning

In many testing situations, differential item functioning (DIF) is a potentially serious problem. It occurs when a test item appears to be easier for one group of examinees than another even after controlling for overall skill level. Differential person functioning (DPF) can occur when "items " can be considered raters and the persons are the objects being rated. This paper introduces the notion of DIF with object-rater data and transposed person-item matrices. The discussion only considers methods for DIF or DPF detection using a binary coding of raters and right-wrong coding of subjects on cognitive tests. Three examples are used: (1) data from a standard setting session of a test of counseling knowledge and skills using an Angoff variation with 9 expert judges or raters; (2) ratings by 14 committee members of 25 research proposals; and (3) data from a mathematics achievement test taken by 384 sixth graders. These examples serve to illustrate the potential utility of DPF, or the application of DIF to rating data and transposed data from cognitive or diagnostic assessment. Notions incorporated in DPF might be especially useful in the area of diagnostic testing. (Contains 4 figures and 17 references.) (SLD) Reproductions supplied by EDRS are the best that can be made from the original document