A new suggestion of criterion score to be used in item discriminaton index

The main purpose of this study, present a new criterion score which using for estimation of item discrimination index and make a comparison between this new criterion score and widely using total test score criterion scores. Due to two different kinds of criterion score comparison, the casual comparative model is used in this research. 80 multiple choice items is also used which belong to 3752 participants of UDS 2005 English test. Two different criterion scores and item discrimination indices which produced by using this criterion scores and upper-lover 27%, point biserial correlations methods compared with dependent samples t-tests. Moreover, correlations between item discrimination is investigated which produced by two different criterion score and a parameters of item response theory to find out which criterion score is more efficient. According to the results of the research, the means of total test score and new criterion score (Weighted criterion score) are different at 0.05 level of significance. Besides, means of item discrimination indices produced by two different criterion score are different at 0.05 level of significance. Finally, Item discrimination indices produced by weighted criterion score has a better correlation with a parameters of item response theory than discrimination indices produced by total test score criteria.