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Difficulty level of the items (p), is assumed to be the same for each item, however, in practice, KR-21 can be applied by finding the average item difficulty across the entirety of the test. KR-21 tends to be a more conservative estimate of reliability than KR-20, which in turn is a more conservative estimate than Cronbach's α .
An example of the CPCs for an item with five categories, scored from 0 to 4, is shown in Figure 1. Figure 1: Rasch category probability curves for an item with five ordered categories. A given threshold partitions the continuum into regions above and below its location. The threshold corresponds with the location on a latent continuum at which ...
The item-total correlation provides an index of the discrimination or differentiating power of the item, and is typically referred to as item discrimination. In addition, these statistics are calculated for each response of the oft-used multiple choice item, which are used to evaluate items and diagnose possible issues, such as a confusing ...
The item-reliability index (IRI) is defined as the product of the point-biserial item-total correlation and the item standard deviation. In classical test theory, the IRI indexes the degree to which an item contributes true score variance to the exam observed score variance. In practice, a negative IRI indicates the relative degree which an ...
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, attitudes, or personality traits, and the item difficulty.
Automatic item generation (AIG), or automated item generation, is a process linking psychometrics with computer programming. It uses a computer algorithm to automatically create test items that are the basic building blocks of a psychological test. The method was first described by John R. Bormuth [1] in the 1960s but was not developed until ...
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An item bank will not only include the text of each item, but also extensive information regarding test development and psychometric characteristics of the items. Examples of such information include: [1] Item author; Date written; Item status (e.g., new, pilot, active, retired) Angoff ratings; Correct answer; Item format; Classical test theory ...