Chapter 6 Evaluation

The properties cut-off Rasch model (c.f. Section 4.8) only hold when the data and model agree. It is, therefore, essential to study and remove discrepancies between model and data. This section explains several techniques that aid in the evaluation of model fit.

• Item fit (6.1)
• Person fit (6.2)
• Differential item functioning (6.3)
• Item information (6.4)
• Reliability (6.5)

These topics address different aspects of the solution. In practice, we have found that item fit is the most critical concern.