Item Response Theory

There are two major theories of measurement in psychometrics: Classical Test Theory (CTT) and Item-Response Theory (IRT). Despite its widespread and long use, CTT has a number of shortcomings, which make it problematic to be used for practical and theoretical purposes. IRT tries to solve these shortcomings, and provide better and more dependable answers. One of the applications of IRT is the assessment of Differential Item Functioning (DIF). DIF tells the test developer whether the test item functions differently for different groups. Another important use of IRT is in the area of Computer Adaptive Tests (CAT). CAT is based on IRT, and the stepping-stone in preparing a CAT is the preparation of an item bank. Item banking is based on IRT. When IRT is ignored, item banking will not be applicable and consequently there will be no CAT.