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).