The item response theory is based on the latent response theory that presents a mathematical relationship between the latent traits and manifestations. It helps in measuring different constructs with the help of analysis, scoring tests, questionnaires, and similar evaluative instruments. The item response theory includes different approaches such as equating process, a multistage approach based, and others to perform tests while considering a common scale as a measure of standard. The main aim of the research is to study the item response theory of test equating for anchor items with the help of empirical selected anchor items based on differential item functioning (DIF). It was found that item response theory plays a vital role in the identification and empirical selection of anchor items. The multistage differential item functioning strategy based on the item response theory is an effective and suitable identifying technique for the anchor items. It was also found that anchor contamination rates decrease as the sample size of the anchor items is increased.

Keywords : Item Response Theory, Anchor Class, Anchor Items, Anchor Selection Strategy, Two-Parameter Model (2PL).