Georg William Rasch () (21 September 1901 – 19 October 1980) was a

Danish Danish may refer to: * Something of, from, or related to the country of Denmark People * A national or citizen of Denmark, also called a "Dane," see Demographics of Denmark * Culture of Denmark * Danish people or Danes, people with a Danish a ...

mathematician A mathematician is someone who uses an extensive knowledge of mathematics in their work, typically to solve mathematical problems. Mathematicians are concerned with numbers, data, quantity, structure, space, models, and change. History On ...

statistician A statistician is a person who works with theoretical or applied statistics. The profession exists in both the private and public sectors. It is common to combine statistical knowledge with expertise in other subjects, and statisticians may wor ...

, and

psychometrician Psychometrics is a field of study within psychology concerned with the theory and technique of measurement. Psychometrics generally refers to specialized fields within psychology and education devoted to testing, measurement, assessment, and ...

, most famous for the development of a class of

measurement Measurement is the quantification of attributes of an object or event, which can be used to compare with other objects or events. In other words, measurement is a process of determining how large or small a physical quantity is as compared ...

models known as

Rasch model The Rasch model, named after Georg Rasch, is a psychometric model for analyzing categorical data, such as answers to questions on a reading assessment or questionnaire responses, as a function of the trade-off between the respondent's abilities, ...

s. He studied with

R.A. Fisher Sir Ronald Aylmer Fisher (17 February 1890 – 29 July 1962) was a British polymath who was active as a mathematician, statistician, biologist, geneticist, and academic. For his work in statistics, he has been described as "a genius who ...

and also briefly with

Ragnar Frisch Ragnar Anton Kittil Frisch (3 March 1895 – 31 January 1973) was an influential Norwegian economist known for being one of the major contributors to establishing economics as a quantitative and statistically informed science in the early 20th ce ...

, and was elected a member of the International Statistical Institute in 1948. In 1919, Rasch began studying mathematics at the

University of Copenhagen The University of Copenhagen ( da, Københavns Universitet, KU) is a prestigious public university, public research university in Copenhagen, Copenhagen, Denmark. Founded in 1479, the University of Copenhagen is the second-oldest university in ...

. He completed a master's degree in 1925 and received a doctorate in science with thesis director

Niels Erik Nørlund Niels Erik Nørlund (26 October 1885, in Slagelse – 4 July 1981, in Copenhagen) was a Danish mathematician. His book ''Vorlesungen über Differenzenrechnung'' (1924, reprinted 1954) was the first book on complex function solutions of dif ...

in 1930. Rasch married in 1928. Unable to find work as a mathematician in the 1930s, he turned to work as a statistical consultant. In this capacity, he worked on a range of problems, including problems of biological growth.

Contributions to psychometrics

Georg Rasch is best known for his contributions to

psychometrics Psychometrics is a field of study within psychology concerned with the theory and technique of measurement. Psychometrics generally refers to specialized fields within psychology and education devoted to testing, measurement, assessment, and ...

. His work in this field began when he used the

Poisson distribution In probability theory and statistics, the Poisson distribution is a discrete probability distribution that expresses the probability of a given number of events occurring in a fixed interval of time or space if these events occur with a known co ...

to model the number of errors made by students when reading texts. He referred to the model as the multiplicative Poisson model. He later developed the

for dichotomous data, which he applied to response data derived from intelligence and attainment tests including data collected by the Danish military. At the same epoch,

American American(s) may refer to: * American, something of, from, or related to the United States of America, commonly known as the "United States" or "America" ** Americans, citizens and nationals of the United States of America ** American ancestry, pe ...

scientists independently developed

item response theory 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 ...

(IRT). Within IRT, the Rasch model is one of the most simple response models. In contrast to other simple models, the Rasch model has a distinctive mathematical property: the model parameters (item difficulties, examinee ability) are sufficient statistics. Rasch demonstrated that his approach met criteria for measurement deduced from an analysis of measurement in the physical sciences. He also proposed generalizations of his model (Rasch, 1960/1980, 1977). Today, the Rasch model is used extensively in assessment in education and

educational psychology Educational psychology is the branch of psychology concerned with the scientific study of human learning. The study of learning processes, from both cognitive and behavioral perspectives, allows researchers to understand individual differences i ...

, particularly for attainment and cognitive assessments.

Major publications

Rasch, G. (1960/1980). ''Probabilistic models for some intelligence and attainment tests''. (Copenhagen, Danish Institute for Educational Research), expanded edition (1980) with foreword and afterword by B.D. Wright. Chicago: The University of Chicago Press. Rasch, G. (1961). On general laws and the meaning of measurement in psychology, pp. 321–334 in ''Proceedings of the Fourth Berkeley Symposium on Mathematical Statistics and Probability'', IV. Berkeley: University of Chicago Press, 1980. Rasch, G. (1977). On Specific Objectivity: An attempt at formalizing the request for generality and validity of scientific statements. ''The Danish Yearbook of Philosophy'', 14, 58-93.

Obituary

Andersen, E. B. (1982) Georg Rasch (1901–1980), ''Psychometrika'', 47,(4), 375-376.

References

External links

*Lina Wøhlk Olsen, ''Essays on Georg Rasch and his contributions to statistics'', PhD thesis Univ. of Copenhagen, in part onlin
here
{{DEFAULTSORT:Rasch, Georg Elected Members of the International Statistical Institute Danish statisticians Psychometricians 1980 deaths 1901 births 20th-century Danish mathematicians