An item response model for testlet-based rating scale items

A new item response model is developed to account for directly for randomness in the threshold and testlet effects in testlet-based rating scale items, which is referred to as the testlet random-effects rating scale model (TRERSM). It is an extension of the random-effects rating scale model (RERSM; Wang, Wilson, & Shih, 2006). Simulations were conducted to examine parameters recovery under the TRERSM by using ConQuest (Wu, Adams, Wilson, & Haldane, 2007). Results indicated that the parameters could be recovered very accurately. An example was provided to demonstrate the advantages of the TRERSM over the RERSM and the rating scale model (RSM; Andrich, 1978).