Rasch Analysis

Rasch analysis can be applied to assessments in a wide range of disciplines, including health studies, education, psychology, marketing, economics and social sciences.

Many assessments in these disciplines involve a well defined group of people responding to a set of items for assessment. Generally, the responses to the items are scored 0, 1 (for two ordered categories); or 0, 1, 2 (for three ordered categories); or 0, 1, 2, 3 (for four ordered categories) and so on, to indicate increasing levels of a response on some variable such as health status or academic achievement. These responses are then added across items to give each person a total score. This total score summarise the responses to all the items, and a person with a higher total score than another one is deemed to show more of the variable assessed. Summing the scores of the items to give a single score for a person implies that the items are intended to measure a single variable, often referred to as a unidimensional variable.

The Rasch model is the only item response theory (IRT) model in which the total score across items characterizes a person totally. It is also the simplest of such models having the minimum of parameters for the person (just one), and just one parameter corresponding to each category of an item. This item parameter is generically referred to as a threshold. There is just one in the case of a dichotomous item, two in the case of three ordered categories, and so on.

1.   What is Rasch Analysis

2.   Why undertake a Rasch analysis?

3.   The research paradigm and the Rasch model

4.   Is there more than one Rasch model?

5.   Different Rasch Model Specifications

6. Thresholds and Steps

One particular difference that has arisen in different Rasch analysis reporting is the use of "step", when the parameters are different across items, and "thresholds", when they are the same across items. This can give the impression that the response process characteristized by the Rasch model is a sequential process. However, the Rasch model is NOT a sequential processing model but a static model, which just specifies the probability of a person with a given location responding, or being classified, in one of the categories of an item.

For example, the term "step" is not used in the dichotomous case because it would imply, implausibly, that a person goes from being wrong to being right, or goes from disagreeing to agreeing. Instead the person is either wrong or right, or either disagrees or agrees; there is no sequential processing here. The response process is a classification into ordered categories defined by thresholds which can be seen as analogous to markings on a ruler except that the thresholds do not have to be equidistant as they are in a ruler - they are estimated. The threshold is the point where the probability of a response in either one of two adjacent categories is 50%.

7.   Disordered Thresholds as an Anomaly

8.   Who should use a Rasch analysis?

9.   An ideal approach to a Rasch analysis?

10. Recommended Rasch Software

11. The RUMM approach to Rasch Analysis

12. What courses and workshops are available on Rasch analysis?

13. What cloud analysis engines and API's are available?

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