The Item Parameters’ Estimation Accuracy In IRT

With the development of psychology metrology, and widely used in various types of psychological and educational tests, the effectiveness and fairness of test has been concerned by educators and psychologists, researching on the item parameters’estimation accuracy and the differential item functioning is more and more in-depth. The is very important to test development, especially to the construction of item bank. Based on the two-parameter Logistic model, delimiting the item parameters’estimation information function firstly, then given the confidence intervals of item parameter estimation, and proposes an IRT-based method for detecting DIF:TL (Two-parameters Likelihood) method. The study is conducted and revealed:(1) The precision of the estimators enhance as the quantity of the sample increases.(2) The examinee’s ability distribution has more influences on difficulty parameter estimation precision, while less influences on discrimination parameter.(3) The estimation precision of item discrimination and item difficulty parameter are both influenced by parameter a and parameter b’s true value.(4) When there are difference between reference and focal groups’ mean ability, the TL’s power are lower than there is a equal mean ability between reference and focal groups.