Georg Rasch

Georg William Rasch was a Danish mathematician, statistician and psychometrician best known for developing the class of measurement models that bear his name, the Rasch models. Educated at the University of Copenhagen and briefly under R.A. Fisher, he applied his models to reading-error data and later to dichotomous test responses, including Danish military intelligence and attainment tests, establishing that item difficulty and examinee ability could be estimated as sufficient statistics independent of the particular sample tested, a foundation of modern educational and psychological assessment.