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A Unified Nonparametric IRT Model for d-Dimensional Psychological Test Data (d-ISOP)

Published online by Cambridge University Press:  01 January 2025

Hartmann Scheiblechner*
Affiliation:
FB Psychologie der Philipps-Universität
*
Requests for reprints should be sent to Hartmann Scheiblechner, FB Psychologie der Philipps-Universität, Gutenbergstraße 18, D-35032 Marburg, Germany. E-mail: scheible@staff.uni-marburg.de.

Abstract

The (univariate) isotonic psychometric (ISOP) model (Scheiblechner, 1995) is a nonparametric IRT model for dichotomous and polytomous (rating scale) psychological test data. A weak subject independence axiom W1 postulates that the subjects are ordered in the same way except for ties (i.e., similarly or isotonically) by all items of a psychological test. A weak item independence axiom W2 postulates that the order of the items is similar for all subjects. Local independence (LI or W3) is assumed in all models. With these axioms, sample-free unidimensional ordinal measurements of items and subjects become feasible. A cancellation axiom (Co) gives, as a result, the additive isotonic psychometric (ADISOP) model and interval scales for subjects and items, and an independence axiom (W4) gives the completely additive isotonic psychometric (CADISOP) model with an interval scale for the response variable (Scheiblechner, 1999). The d-ISOP, d-ADISOP, and d-CADISOP models are generalizations to d-dimensional dependent variables (e.g., speed and accuracy of response).

Information

Type
Original Paper
Copyright
Copyright © 2007 The Psychometric Society

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