ABSTRACT
Classical test theory has been in place for nearly a century and has been very serviceable. However, it is not much of a theory; https://www.w3.org/1998/Math/MathML"> x = t + e https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9780203052358/4d8d47ca-25d0-4bdc-8efc-e65415dedec9/content/inline-math_26_B.tif" xmlns:xlink="https://www.w3.org/1999/xlink"/> is about as simple as a theory could be. Yet its simplicity permits easy extension and amplification. Item response theory (IRT), which has been a serious contender for only about two decades, is much stronger, but with its strength comes constraint. Item response theory applies to dichotomously scored items; extending it to more complicated situations takes work.
