Ok I know it’s the item characteristic curve of the 1PL model. What then? [img src] Mysterious Item Response Theory Item response theory is mysterious and intimidating to students. It is mysterious in the way it is presented in textbooks, at least in introductory ones. The text often starts with an ambitious conceptual introduction to IRT, which most students would be able to follow, but with some confusion. Curious students might bear with the confusion and expect it to resolve in the following text, only to find themselves …