General polytomous testlet model

Research Method · All research methods
Evidence · 6 claims (4 for, 1 mixed, 1 against) · 2 studies (1 design, 1 theoretical), q2 · 0 of 2 report an effect size · 6 claims rest on one study

Description

The general polytomous testlet model is an item response theory model for testlet-based tests containing both dichotomously and polytomously scored items. It extends the general testlet model of Li, Bolt, and Fu (2006), which the report notes "is essentially the same as the bifactor model", by using a generalized partial credit model for the polytomous items. Each item loads on a general ability dimension and on a secondary dimension associated with its testlet, with separate discrimination parameters for the two factors. According to the report, "This model not only takes into account local dependence within the testlets but also provides more information about how items within a testlet ar

Accounts

• General polytomous testlet model: a bifactor-style IRT model extending the general testlet model to mixed dichotomous and polytomous testlet items via a generalized partial credit model: The general polytomous testlet model is an item response theory model for testlet-based tests containing both dichotomously and polytomously scored items. It extends the general testlet model of Li, Bolt, and Fu (2006), which the report notes "is essentially the same as the bifactor model", by using a generalized partial credit model for the polytomous items. Each item loads on a general ability dimension and on a secondary dimension associated with its testlet, with separate discrimination parameters for the two factors. According to the report, "This model not only takes into account local dependence within the testlets but also provides more information about how items within a testlet ar (Yanmei Li et al. (2010))

Claims

• The general polytomous testlet model recovers true item parameters well in simulation, with average correlations of 0.9680, 0.8608, and 0.9982 for discrimination and difficulty parameters [+M]
• A multidimensional IRT model with simple structure fits testlet-based reading data better than both the general polytomous testlet model and the standard 2PL/GPCM [-M]
• In simulation, ignoring local dependence overestimates reliability, and the overestimation grows with the size of the testlet effect (17.0%-21.8% decrease under the larger testlet effect vs. 4.8%-7.4% under the small) [+W]
• In operational reading-test data, item parameter estimates from a standard 2PL/GPCM that ignores local dependence closely match those from the testlet model (average correlations 0.9893 and 0.9978) [+W]
• In operational reading-test data, ignoring local dependence inflates reliability estimates, with passage-based alpha 2.3%-4.9% lower than item-based alpha across six test forms [+W]
• The proportionality restrictions that the testlet model imposes on the bifactor model were implausible in the applied dataset, as specific-to-general loading quotients varied far from constant within testlets [~W]

Related Research Methods

• Matrix sampling with planned missingness in large-scale assessments

Key Sources

• Yanmei Li, Shuhong Li, and Lin Wang. (2010). Application of a General Polytomous Testlet Model to the Reading Section of a Large-Scale English Language Assessment. ETS Research Report RR-10-21. http://www.ets.org/research/contact.html

Page metadata

Field	Value
type	research-method
id	general-polytomous-testlet-model
title	General polytomous testlet model
description	The general polytomous testlet model is an item response theory model for testlet-based tests containing both dichotomously and polytomously scored items.
status	review
moved_from	theory/general-polytomous-testlet-model
generated	by process:sweep-kinds on 2026-10-10
trust	unverified — no one has confirmed this page's content
sources	1 — yanmei-li-2010

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