The Rasch testlet model for both dichotomous and polytomous items in testlet-based tests is proposed. It can be viewed as a special case of the multidimensional random coefficients multinomial logit model (MRCMLM). Therefore, the estimation procedures for the MRCMLM can be directly applied. Simulations were conducted to examine parameter recovery…

The random-effects facet model that deals with local item dependence in many-facet contexts is presented. It can be viewed as a special case of the multidimensional random coefficients multinomial logit model (MRCMLM) so that the estimation procedures for the MRCMLM can be directly applied. Simulations were conducted to examine parameter recovery…

This study presents the random-effects rating scale model (RE-RSM) which takes into account randomness in the thresholds over persons by treating them as random-effects and adding a random variable for each threshold in the rating scale model (RSM) (Andrich, 1978). The RE-RSM turns out to be a special case of the multidimensional random…

This study presents a procedure for detecting differential item functioning (DIF) for dichotomous and polytomous items in testlet-based tests, whereby DIF is taken into account by adding DIF parameters into the Rasch testlet model. Simulations were conducted to assess recovery of the DIF and other parameters. Two independent variables, test type…

A parallel design, in which items across different scales within an instrument share common stimuli and subjects respond to the common stimulus for each scale, is sometimes used in questionnaires or inventories. Because the items across scales share the same stimuli, the assumption of local item independence may not hold, thereby violating the…