Assessing the impact of uniform and nonuniform differential item functioning items on Rasch measure: the polytomous case

Differential item functioning (DIF) is understood to be present when something about the characteristics of a subject interferes with the relationship between ability and item responses. When DIF items are present in a questionnaire, an impact on the estimated ability measure can be expected. The aim of this paper is to investigate the impact of uniform and nonuniform DIF items on the measures obtained when applying the Rating Scale Model making use of a simulation study.