In psychometrics, item response theory (IRT), also known as latent trait theory, strong true score theory, or modern mental test theory, is a paradigm for the design, analysis, and scoring of tests, questionnaires, and similar instruments measuring abilities, attitudes, or other variables. Unlike simpler alternatives for creating scales evaluating questionnaire responses it does not assume that each item is equally difficult. This distinguishes IRT from, for instance, the assumption in Likert scaling that "All items are assumed to be replications of each other or in other words items are considered to be parallel instruments" (p. 197). By contrast, item response theory treats the difficulty of each item (the ICCs) as information to be incorporated in scaling items. ICC stands for item characteristic curve.