The Effect of Item Characteristics and Persons Ability Levels on the Assumption of Local Independence in Item Response Theory

Abstract

This study aimed at investigating the effect of item characteristics and persons, ability level on item local independence. To achieve the aim of the study, responses of (1000) persons were generated on (100) items and were analyzed using the two-parameter logistic model to find the parameters of the items and the ability of persons. Four forms of tests were formed according to the level of difficulty and discrimination of the item, and persons were divided into three levels of ability. The results of the study showed that the percentage of item pairs that violate the assumption of local independence was the highest in the case of the first form (high difficult, high discriminate) at the high ability and the lowest at low ability level. The results also indicated that the percentage of item pairs that violate the assumption of local independence increased by increasing the ability level in the first form, whereas it decreased in the fourth form (low difficult, low discriminate). In general, the results showed the item characteristics and the persons ability level influenced the assumption of local independence. The discrimination of the item had a greater role in influencing it than the difficulty of the item by testing the significance of statistical differences between the percentages of item pairs to the assumption of local independence according to the persons ability level and the test form