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

7. Disordered Thresholds as an Anomaly

As in the case of a ruler, thresholds marking off successive categories need to be ordered to be interpretable. However, in estimating the thresholds from the data, it is possible to discover that the estimates are not properly ordered. This is a sign that the categories are not working as intended and an anomaly in the data that needs to be understood and corrected is disclosed.

Prior to the work of Rasch, Thurstone had constructed a model for ordered categories which also involved thresholds. These may be derived from the Rasch thresholds. The problem with the Thurstone thresholds is that they are always ordered as a property of the model no matter what the features of the data - they have no use in disclosing whether categories are working in the ordering intended. Thurstone thresholds cannot disclose any anomalies in the ordering; indeed they will hide them.

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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