Using IRT: analysis of the response categories and performing Rasch analysis
We also performed Rasch analysis in order to confirm unidimensionality, and to determine the model fit, the monotonicity, the local independence and the Differential Item Functioning (DIF). In general, a minimum of ten observations per category per item is recommended in order to reach a stable estimation of category thresholds [According to the COSMIN criteria for a sufficient structural validity rating the following requirements must be fulfilled: an adequate model fit, no violation of monotonicity, unidimensionality and local independence [