Computerized adaptive testing for testlet-based innovative items

Increasing use of innovative items in operational assessments has shedded new light on the polytomous testlet models. In this study, we examine performance of several scoring models when polytomous items exhibit random testlet effects. Four models are considered for investigation: the partial credit model (PCM), testlet-as-a-polytomous-item model (TPIM), random-effect testlet model (RTM), and fixed-effect testlet model (FTM). The performance of the models was evaluated in two adaptive testings where testlets have nonzero random effects. The outcomes of the study suggest that, despite the manifest random testlet effects, PCM, FTM, and RTM perform comparably in trait recovery and examinee classification. The overall accuracy of PCM and FTM in trait inference was comparable to that of RTM. TPIM consistently underestimated population variance and led to significant overestimation of measurement precision, showing limited utility for operational use. The results of the study provide practical implications for using the polytomous testlet scoring models.