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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.
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 ...
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 abilities, attitudes, or other variables.
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 .
Weakly correlate with the totality of the remaining items, reflected in an increase in Cronbach's alpha if the item is eliminated from the test; In practical test construction, item analysis is an iterative process, and cannot be entirely automated. The psychometrician's judgement is required to determine whether the emerging set of items to be ...
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 value assigned to each Likert item is simply determined by the researcher designing the survey, who makes the decision based on a desired level of detail. However, by convention Likert items tend to be assigned progressive positive integer values. Likert scales typically range from 2 to 10 – with 3, 5, or, 7 being the most common. [14]
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 ...