deltaPlotR: An R Package for Differential Item Functioning Analysis with Angoff's Delta Plot

Abstract

Angoff's delta plot is a straightforward and not computationally intensive method to identify differential item functioning (DIF) among dichotomously scored items. This approach was recently improved by proposing an optimal threshold selection and by considering several item purification processes. Moreover, to support practical DIF analyses with the delta plot and these improvements, the R package deltaPlotR was also developed. The purpose of this paper is twofold: to outline the delta plot by describing the original method and its recent improvements in a user-oriented way, and to illustrate the structure and performances of the deltaPlotR package. A real data set about language skill assessment is being analyzed as an illustrative example.