Violation of Conditional Independence in the Many-Facets Rasch Model

ABSTRACT Estimation of parameters for the many-facets Rasch model requires that conditional on the values of the facets, such as person ability, item difficulty, and rater severity, the observed responses within each facet are independent. This requirement has often been discussed for the Rasch models and 2PL and 3PL models, but it becomes more complex with more facets. To show how violation of conditional independence may be exhibited, three scenarios with different types of dependency are developed: (a) raters rating the same work, (b) a residual ability shared by two tasks, and (c) score on one task dependent on observed score on a previous task.