Many Facet, Common Latent Trait Polytomous IRT Model and EM Algorithm

2000 Mathematics Subject Classification: 91E45.

There are many areas of assessment where the level of performance can not be determined using ordinal, “objective” test. For example, there are aspects of writing language skills which should be subjectively qualified by judges based on some criteria. Usually such data is studied using the Many Facet Rasch Model. To address the problem with Item Response Theory (IRT) approach a Many Facet IRT model for polytomous item response in the case of common latent trait is presented. For estimation of the parameters of the model the EM-algorithm is derived.