Rasch model
![Figure 1: Test characteristic curve showing the relationship between total score on a test and person location estimate](/Images/godic/202502/06/TCC4249.PNG")
![Figure 2: Graph showing histograms of person distribution (top) and item distribution (bottom) on a scale](/Images/godic/202502/06/PersItm4249.PNG")
![Figure 3: ICCs for a number of items. ICCs are coloured to highlight the change in the probability of a successful response for a person with ability location at the vertical line. The person is likely to respond correctly to the easiest items (with locations to the left and higher curves) and unlikely to respond correctly to difficult items (locations to the right and lower curves).](/Images/godic/202502/06/ICCs_prog4249.png")
![Figure 4: ICC for the Rasch model showing the comparison between observed and expected proportions correct for five Class Intervals of persons](/Images/godic/202502/06/RaschICC4249.gif")
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 (a) the respondent's abilities, attitudes or personality traits and (b) the item difficulty. For example, they may be used to estimate a student's reading ability, or the extremity of a person's attitude to capital punishment from responses on a questionnaire. In addition to psychometrics and educational research, the Rasch model and its extensions are used in other areas, including the health profession and market research because of their general applicability.