Parameters Estimation Of IRT Multicategory Scoring Item

Although the establishment of examination system origins from China, and after several thousand years of practices, each country throughout the world adopted this system one after another, and as a choosing basis for the civil official system, China have never been carried out relatively scientific quantificational analysis aimed at examination, which result in that the development of modern psychometrics was develop in foreign country and did not bring in China until the westernize culture prevailing in the east. Psychometrics is a science studied in the aspects of psychological testing and assessment, and is the knowledge including the research range of quantitative psychology, individual differences and mental test theories and so on. The development of psychometrics has gone through two major phase: classical test theory phase (Shorted for CTT) and modern test theory phase. In the theory of CTT, researchers develop the conceptual system such as reliability, validity, difficulty and discrimination etc. with the basis of the truth value theory of scores, with which to test the quality of measuring tools or the examination questions. Since the 1960s to 1970s, the modern test theory with the item response theory at the core has become the nucleus content of the psychometrics research. Comparing to the CTT, the item response theory has obvious advantages, the item parameter it adopts(such as difficulty, discrimination and guess index and so on) is a kind of indicator which not affected by sample. The obtainment of these parameters is not differed from the changes in the subjects sample who receive the test; meanwhile, the estimation to the ability of subject will not differ from the difference of the examination questions, etc. as a result of these advantages in the item response theory, it is widely used in the psychological test and in the fields of examination.In spite of that the item response theory has incomparable advantages which not assumed by the CTT, the estimation of parameter in the item response theory is very complex as each gradation of every item is correspondence with its difficulty and discrimination, thus adds the difficulty in estimation. Therefore, this theory is not applied very well all the time. The thesis will try to overcome the estimation difficulty through dividing the subjects into groups, and give preliminary discussion and probe into this problem.