Everybody knows what IRT is... (really?)

Item response theory (IRT) is not only a famous acronym, it also covers a broad range of statistical and psychometric models, methods, and applications in psychology and educational science. However, IRT looks somewhat misunderstood or even esoteric to the non-statisticians and non-psychometricians. The main goal of this talk is to briefly and clearly present the main aspects of traditional IRT: objectives, assumptions, basic models, and basic estimation methods. As a secondary purpose, extensions of IRT to more complex situations (polytomous data, multidimensional and hierarchical models, computerized adaptive testing, differential item functioning, nonparametric IRT) are briefly outlined. This talk will be as little technical as possible, focusing on the main concepts and applications of this theory.