Within psychometrics, Item analysis refers to statistical methods used for selecting test items for inclusion in a psychological test. The concept goes back at least to Guilford (1936). The process of item analysis varies depending on the psychometric model. For example, classical test theory or the Rasch model call for different procedures. In all cases, however, the purpose of item analysis is to produce a relatively short list of items that constitute a pure but comprehensive test of one or a few psychological constructs.