The study of item functional difference (IFD) started in the middle of this century in America. In educational assessment, both the assessor and assessee are faced with the existence of IFD. Now IFD has attracted more and more attention with the development of standardized testing.The author gives a general account of the study of IFD, its background, its definition, the difference betWeen IFD and systematic error, the relationship between IFD and dimension, analyzing approach and princiPles, etc. She also relate IFD to RT'VU's testing.
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