The Item Parameters’ Estimation Accuracy of Two-Parameter Logistic Model

Abstract

The item parameters' estimation accuracy is very important to test development, especially to the construction of item bank. Nowadays, in domestic and foreign, the study of item parameters' estimation accuracy is mostly based on that the true values of the item parameters are known, under this circumstances,applying kinds of estimation methods to estimate new estimators, then evaluating methods' effectiveness by comparison with the true values about the root-mean-square-error(RMSE) and Bias. But this method can't present the change rules of estimation error among the different parameters' true values. In order to solve this problem, this article attempts to explore the item parameters' estimation accuracy issue on the point of item parameters estimation information function.Based on the two-parameter Logistic model, given the definition of the item parameters' estimation information function firstly, then generated examinee sample to explore the factors which affected item parameters' estimation accuracy by computer simulation randomly. The experiments were designed(2 × 3 × 2)cases. The study is conducted and revealed:(1) The accuracy of the estimators enhance as the quantity of the sample increases.(2) The examinee's ability distribution has more influences on difficulty parameter estimation accuracy, while less influences on discrimination parameter.(3) The estimation accuracy of item discrimination and item difficulty parameter are both influenced by parameter a and parameter b's true value.