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?

A researcher who is developing items of a test or questionnaire intending to sum the scores on the items can use a Rasch model analysis to check the degree to which this scoring and summing is defensible in the data collected. For example, if two groups are to be compared on the variable of interest (e.g. males and females), it is important to demonstrate that the workings of the items is the same in the two groups. Working in the same way permits interpreting the total score as meaning the same in the two groups.

In checking how well the data fit the model, it is important to be able to diagnose very quickly where the misfit is the worst, and then proceed to try to understand this misfit in terms of the construction of the items and the understanding of the variable in terms of its theoretical development.

A very important part of the Rasch analysis from this perspective is to be in dynamic and interactive control of an analysis and to be able to follow the evidence to see where the responses may be invalid.

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

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?

 

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