Rasch Model

The Rasch model, named for Georg Rasch, is a psychometric model for analyzing categorical data, such as answers to questions on a reading assessment or a questionnaire, as a function of the trade-off between a respondent's ability, attitude or personality trait and the difficulty of the item being answered, and it can be used, for example, to estimate a student's reading ability or the extremity of a person's attitude toward a topic from a set of questionnaire responses. Beyond psychometrics and educational research, the Rasch model and its extensions are also used in the health professions, agriculture and market research. The mathematics underlying the Rasch model is a special case of item response theory, but there are important differences in how its parameters are interpreted and in its philosophical implications, centered on specific objectivity, a defining property that Georg Rasch treated as a requirement for successful measurement, that separate proponents of the Rasch model from the broader item response modeling tradition.