Analysis of C-Tests with the Equidistance and the Dispersion Models

C-tests are commonly used as measures of second language reading comprehension and general language proficiency. Analysis of C-tests with item response theory models is problematic due to the interdependent structure of C-test items or gaps. An approach to facilitate item response theory (IRT) analysis of C-tests involves treating each passage as a polytomous super-item. This approach facilitates the application of polyomous IRT models for ordered response data to the C-test passages. Usually, Andrich’s rating scale model or Masters (۱۹۸۲) partial credit model are used to analyse the data. In this study, we aim to employ two alternative modelling techniques, namely, the equidistant model (Andrich, ۱۹۸۲) and the dispersion model (Rost, ۱۹۸۸) to C-test data. Our findings showed that the C-test data have a good fit to the both models and can be used for psychometric analysis of C-test passages. Information criteria showed that the dispersion model has a better fit compared to the equidistance model.

Keywords:

C-test , Dispersion model , equidistance model , Local item dependence , polytomous Rasch models