Abstract
Educational assessments tests are often constructed using testlets because of the flexibility to test various aspects of the cognitive activities and broad content sampling. However, the violation of the local item independence assumption is inevitable when tests are built using testlet items. In this study, simulations are conducted to evaluate the performance of item response theory models and testlet response theory models for both the dichotomous and polytomous items in the context of equating tests composed of testlets. We also examine the impact of testlet effect, length of testlet items, and sample size on estimating item and person parameters. The results show that more accurate performance of testlet response theory models over item response theory models was consistently observed across the studies, which supports the benefits of using the testlet response theory models in equating for tests composed of testlets. Further, results of the study indicate that when sample size is large, item response theory models performed similarly to testlet response theory models across all studies.
Highlights
In the current practice of educational measurement, test equating is a vital step to put scores from different forms onto a same scale
We compared the performance of item response theory (IRT) models and testlet response theory (TRT) models for the dichotomous and polytomous items in the context of equating tests composed of testlets
For achieving the most generalization, in this study, the 2PL and the TRT model were selected as the item response functions for the dichotomous items, and the graded response model (GRM) and graded response testlet model (GRTM) model were selected as the item response functions for the polytomous items
Summary
In the current practice of educational measurement, test equating is a vital step to put scores from different forms onto a same scale. In most large-scale testing programs, it is common for a standardized test to consist of testlets (Bradlow et al, 1999; Rijmen, 2009; Cao et al, 2014; Tao and Cao, 2016). A testlet is defined as an aggregation of items which are based on a common stimulus (Wainer and Kiely, 1987; Bradlow et al, 1999). Researchers have conducted an abundance of studies to propose different approaches to handle local item dependence (LID), little research in the literature has focused on the performance of different approaches to accommodate LID on testlet-based test equating
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